Trapping of hemiquinone radicals at Mo and P sites by phosphide-bridged dimolybdenum species: chemistry of complexes [Mo2(eta5-C5H5)2(OC6H4OH)(mu-PR2)(CO)4] and [Mo2(eta5-C5H5)2{mu-PR(OC6H4OH)}(CO)4]- (R = Cy, Ph)

The phosphide-bridged dimolybdenum complexes (H-DBU)[Mo2Cp2(mu-PR2)(CO)4] (R= Cy, Ph; DBU = 1,8-diazabicyclo[5.4.0.]undec-7-ene) react with p-benzoquinone to give the hemiquinone complexes [Mo(2)Cp2(OC6H4OH)(mu-PR2)(CO)4]. The latter experience facile homolytic cleavage of the corresponding Mo-O bonds and react readily at room temperature with HSPh or S2Ph2 to give the thiolate complexes [Mo2Cp2(mu-PCy2)(mu-SPh)(CO)4] or [Mo2Cp2(mu-PR2)(mu-SPh)(CO)2]. In contrast, PRH-bridged substrates experience overall insertion of quinone into the P-H bond to give the anionic compounds (H-DBU)[Mo(2)Cp2{mu-PR(OC6H4OH)}(CO)4], which upon acidification yield the corresponding neutral hydrides. The cyclohexyl anion experiences rapid nucleophilic displacement of the hemiquinone group by different anions ER- (ER = OH, OMe, OC4H5, OPh, SPh) to give novel anionic compounds (H-DBU)[Mo2Cp2{mu-PCy(ER)}(CO)4], which upon acidification yield the corresponding neutral hydrides. The structure of four of these hydride complexes [PPh(OC6H4OH), PCy(OH), PCy(OMe), and PCy(OPh) bridges] was determined by X-ray diffraction methods and confirmed the presence of cis and trans isomers in several of these complexes. In addition, it was found that the hydroxyphosphide anion [Mo2Cp2{mu-PCy(OH)}(CO)4]- displays in solution an unprecedented tautomeric equilibrium with its hydride-oxophosphinidene isomer [Mo2Cp2(mu-H){mu-PCy(O)}(CO)4]-.     

Proton induced P-H and Mo-H bond activation at the phosphide bridged dimolybdenum complexes [Mo2Cp2(mu-H)(mu-PHR)(CO)4](R = Cy, 2,4,6-C6H2R'3; R'= H, Me, tBu)

The new hydride complexes [Mo2Cp2(mu-H)(mu-PHR)(CO)4] having bulky substituents (R = 2,4,6-C(6)H2tBu3= Mes*, R = 2,4,6-C6H2Me3= Mes) have been prepared in good yield by addition of Li[PHR] to the triply bonded [Mo2Cp2(CO)4] and further protonation of the resulting anionic phosphide complex [Mo2Cp2(mu-PHR)(CO)4]-. Protonation of the Mes* compound with either [H(OEt2)2][B{3,5-C6H3(CF3)2}4] or HBF4.OEt2 gives the cationic phosphinidene complex [Mo2Cp2(mu-H)(mu-PMes*)(CO)4]+ in high yield. In contrast, protonation of the analogous hydride compounds with Mes or Cy substituents on phosphorus give the corresponding unsaturated tetracarbonyls [Mo2Cp2(mu-PHR)(CO)4]+, which are unstable at room temperature and display a cis geometry. Decomposition of the latter give the electron-precise pentacarbonyls [Mo2Cp2(mu-PHR)(mu-CO)(CO)4]+, also displaying a cis arrangement of the metal fragments. In the presence of BF4- as external anion, fluoride abstraction competes with carbonylation to yield the neutral fluorophosphide hydrides [Mo2Cp2(mu-H)(mu-PFR)(CO)4]. Similar results were obtained in the protonation reactions of the hydride compounds having a Ph substituent on phosphorus. In that case, using HCl as protonation reagent gave the chloro-complex [Mo2ClCp2(mu-PHPh)(CO)4] in good yield. The structures and dynamic behaviour of the new compounds are analyzed on the basis of solution IR and 1H, 31P, 19F and 13C NMR data as well as the X-ray studies carried out on [Mo2Cp2(mu-H)(mu-PHMes)(CO)4](cis isomer), [Mo2Cp2(mu-H)(mu-PFMes)(CO)4](trans isomer), [Mo2Cp2(mu-PHCy)(mu-CO)(CO)4](BF4) and [Mo2ClCp2(mu-PHPh)(CO)4].     

Ten-electron coordination and reactivity of an arylphosphinidene ligand

Photochemical decarbonylation of [Mo2Cp2(mu-PR*)(CO)4] (Cp = eta5-C5H5; R* = 2,4,6-C6H2tBu3) gives [Mo2Cp2(mu-kappa1:kappa1,eta6-PR*)(CO)2], which shows the first example of a remarkable 10-electron donor arylphosphinidene ligand which bridges two Mo atoms through its phosphorus atom while being pi-bonded to one Mo center through the six carbon atoms of the aryl ring. This causes a severe pyramidal distortion of the P-bound C atom. The complex adds CO to give [Mo2Cp2(mu-kappa1:kappa1,eta4-PR*)(CO)3], which has an 8-electron donor PR* ligand, and then the parent complex [Mo2Cp2(mu-PR*)(CO)4]. Protonation of [Mo2Cp2(mu-kappa1:kappa1,eta6-PR*)(CO)2] gives the hydride [Mo2Cp2(H)(mu-kappa1:kappa1,eta6-PR*)(CO)2]+, which undergoes P-C bond cleavage and hydride migration, affording the phosphido cation [Mo2Cp2(mu-P)(eta6-R*H)(CO)2]+.     

High yield synthesis and reactivity of a phosphinidene bridged dimolybdenum complex

Protonation of [Mo2Cp2(mu-H)(mu-PHR*)(CO)4] (Cp = eta5-C5H5, R* = 2,4,6-C6H2tBu3) with HBF4.OEt2 gives the hydridophosphinidene complex [Mo2Cp2(mu-H)(mu-PR*)(CO)4]BF4, which is easily deprotonated with H2O to give the known phosphinidene complex [Mo2Cp2(mu-PR*)(CO)4] in 95% yield. Reaction of the latter with I2 gives the unsaturated phosphinidene complex [Mo2Cp2I2(mu-PR*)(CO)2], which exhibits an intermetallic distance of 2.960(2) A. Irradiation of solutions of [Mo2Cp2(mu-PR*)(CO)4] with UV light gives a mixture of the triply bonded [Mo2Cp2(mu-PR*)(mu-CO)2] and the hydridophosphido derivative [Mo2Cp2(mu-H){mu-P(CH2CMe2)C6H2tBu2}(CO)4] as major species. The latter complex results from an intramolecular C-H bond cleavage from a tBu group and has been characterized by spectroscopy and an X-ray study. Irradiation in the presence of HCC(p-tol) results in the insertion of the alkyne into the Mo-P bond to give [Mo2Cp2{mu-eta1:eta2,kappa-C(p-tol)CHPR*}(CO)4] structurally characterized through an X-ray study.     

Hydride transfer reactivity of tetrakis(trimethylphosphine)(hydrido)(nitrosyl)molybdenum(0)

The tetrakis(trimethylphosphine) molybdenum nitrosyl hydrido complex trans-Mo(PMe(3))(4)(H)(NO) (2) and the related deuteride complex trans-Mo(PMe(3))(4)(D)(NO) (2a) were prepared from trans-Mo(PMe(3))(4)(Cl)(NO) (1). From (2)H T(1 min) measurements and solid-state (2)H NMR the bond ionicities of 2a could be determined and were found to be 80.0% and 75.3%, respectively, indicating a very polar Mo--D bond. The enhanced hydridicity of 2 is reflected in its very high propensity to undergo hydride transfer reactions. 2 was thus reacted with acetone, acetophenone, and benzophenone to afford the corresponding alkoxide complexes trans-Mo(NO)(PMe(3))(4)(OCHR'R') (R' = R' = Me (3); R' = Me, R' = Ph (4); R' = R' = Ph (5)). The reaction of 2 with CO(2) led to the formation of the formato-O-complex Mo(NO)(OCHO)(PMe(3))(4) (6). The reaction of with HOSO(2)CF(3) produced the anion coordinated complex Mo(NO)(PMe(3))(4)(OSO(2)CF(3)) (7), and the reaction with [H(Et(2)O)(2)][BAr(F)(4)] with an excess of PMe(3) produced the pentakis(trimethylphosphine) coordinated compound [Mo(NO)(PMe(3))(5)][BAr(F)(4)] (8). Imine insertions into the Mo-H bond of 2 were also accomplished. PhCH[double bond, length as m-dash]NPh (N-benzylideneaniline) and C(10)H(7)CH=NPh (N-1-naphthylideneaniline) afforded the amido compounds Mo(NO)(PMe(3))(4)[NR'(CH(2)R')] (R' = R' = Ph (9), R' = Ph, R' = naphthyl (11)). 9 could not be obtained in pure form, however, its structure was assigned by spectroscopic means. At room temperature 11 reacted further to lose one PMe(3) forming 12 (Mo(NO)PMe(3))(3)[N(Ph)CH(2)C(10)H(6))]) with agostic stabilization. In a subsequent step oxidative addition of the agostic naphthyl C-H bond to the molybdenum centre occurred. Then hydrogen migration took place giving the chelate amine complex Mo(NO)(PMe(3))(3)[NH(Ph)(CH(2)C(10)H(6))] (15). The insertion reaction of 2 with C(10)H(7)N=CHPh led to formation of the agostic compound Mo(NO)(PMe(3))(3)[N(CH(2)Ph)(C(10)H(7))] (10). Based on the knowledge of facile formation of agostic compounds the catalytic hydrogenation of C(10)H(7)N=CHPh and PhN=CHC(10)H(7) with 2 (5 mol%) was tested. The best conversion rates were obtained in the presence of an excess of PMe(3), which were 18.4% and 100% for C(10)H(7)N=CHPh and PhN=CHC(10)H(7), respectively.     

The synthesis of [FeRu(CO)2(mu-CO)2(eta-C5H5)(eta-C5Me5)] and convenient entries to its organometallic chemistry

The synthesis, fluxionality and reactivity of the heterobimetallic complex [FeRu(CO)2(mu-CO)2(eta-C5H5)(eta-C5Me5)] are described. Complex exhibits enhanced photolytic reactivity towards alkynes compared to its homometallic analogues, forming the dimetallacyclopentenone complexes [FeRu(CO)(mu-CO){mu-eta]1:eta3-C(O)CR"CR'}eta]-C5H5)(eta-C5Me5)]( R'= R"= H; R'= R"= CO2Me; R'= H, R"= CMe2OH). Prolonged photolysis with diphenylethyne gives the dimetallatetrahedrane complex [FeRu(mu-CO)(mu-eta2:eta2-CPhCPh)(eta-C5H5)(eta-C5Me5)], which contains the first iron-ruthenium double bond. Complexes containing a number of organic fragments can be synthesised using , and . Heating a solution of gave the alkenylidene complex [FeRu(CO)2(mu-CO){mu-eta]1:eta2-C=C(CO2Me)2}(eta-C5H5)(eta-C5Me5)] through an unusual methylcarboxylate migration. Protonation and then addition of hydride to gives the ethylidene complex [FeRu(CO)2(mu-CO)(mu-CHCH3)(eta-C5H5)(eta-C5Me5)] via the ionic vinyl species [FeRu(CO)2(mu-CO)(mu-eta]1:eta2-CH=CH2)(eta-C5H5)(eta-C5Me5)][BF4]. Compound exhibits cis/trans isomerisation at room temperature. Protonation of dimetallacyclopentenone complexes gives the allenyl species [FeRu(CO)2(mu-CO)(mu-eta1:eta2-CH=C=CMe2)(eta-C5H5)(eta-C5Me5)][BF4]. Compound exist as three isomers, two cis and one trans. The two cis isomers are shown to be interconverting by sigma-pi isomerisation. The solid state structures of these compounds were established by X-ray crystallography and are discussed.     

Structural consequences of the one-electron reduction of d4 [Mo(CO)2(eta-PhC[triple bond]CPh)Tp']+ and the electronic structure of the d5 radicals [M(CO)L(eta-MeC[triple bond]CMe)Tp'] {L = CO and P(OCH2)3CEt}

Reduction of [M(CO)2(eta-RC[triple bond]CR')Tp']X {Tp' = hydrotris(3,5-dimethylpyrazolyl)borate, M = Mo, X = [PF6]-, R = R' = Ph, C6H4OMe-4 or Me; R = Ph, R' = H; M = W, X = [BF4]-, R = R' = Ph or Me; R = Ph, R' = H} with [Co(eta-C5H5)2] gave paramagnetic [M(CO)2(eta-RC[triple bond]CR')Tp'], characterised by IR and ESR spectroscopy. X-Ray structural studies on the redox pair [Mo(CO)2(eta-PhC[triple bond]CPh)Tp'] and [Mo(CO)2(eta-PhC[triple bond]CPh)Tp'][PF6] showed that oxidation is accompanied by a lengthening of the C[triple bond]C bond and shortening of the Mo-C(alkyne) bonds, consistent with removal of an electron from an orbital antibonding with respect to the Mo-alkyne bond, and with conversion of the alkyne from a three- to a four-electron donor. Reduction of [Mo(CO)(NCMe)(eta-MeC[triple bond]CMe)Tp'][PF6] with [Co(eta-C5H5)2] in CH2Cl2 gives [MoCl(CO)(eta-MeC[triple bond]CMe)Tp'], via nitrile substitution in [Mo(CO)(NCMe)(eta-MeC[triple bond]CMe)Tp'], whereas a similar reaction with [M(CO){P(OCH2)3CEt}(eta-MeC[triple bond]CMe)Tp']+ (M = Mo or W) gives the phosphite-containing radicals [M(CO){P(OCH2)3CEt}(eta-MeC[triple bond]CMe)Tp']. ESR spectroscopic studies and DFT calculations on [M(CO)L(eta-MeC[triple bond]CMe)Tp'] {M = Mo or W, L = CO or P(OCH2)3CEt} show the SOMO of the neutral d5 species (the LUMO of the d4 cations) to be largely d(yz) in character although much more delocalised in the W complexes. Non-coincidence effects between the g and metal hyperfine matrices in the Mo spectra indicate hybridisation of the metal d-orbitals in the SOMO, consistent with a rotation of the coordinated alkyne about the M-C2 axis.     

Base induced P-C bond cleavage in a coordinated bis(dimethylphosphino)methane ligand

Treatment of fac-[Mn(CNR)(CO)3{(PMe2)2CH2}]ClO4 (1a R = Ph, R = tBu) with KOH produced the cleavage of one of the P-C bonds of the coordinated dmpm ligand, resulting in the formation of phosphine-phosphinite complexes fac-[Mn(PMe2O)(CNR)(CO)3(PMe3)] (2a,b). Alkoxides such as NaOMe and NaOEt promoted similar processes in 1a,b, yielding fac-[Mn(CNR)(CO)3(PMe3)(PMe2OR')]ClO4 (3a R = tBu, R' = Me; 3b R = Ph, R' = Me; 4a R = tBu, R' = Et; 4b R = Ph, R' = Et) derivatives. The phosphinite ligand in 2a, b can be sequentially protonated by addition of 0.5 and 1 equivalent of HBF4 leading to fac-[{Mn(CNR)(CO)3(PMe3)(PMe2O)}2H]BF4 (6a,b) and fac-[Mn(CNR)(CO)3(PMe3)(PMe2OH)]BF4 (5a,b), respectively.     

Heterometallic cluster complexes (RhMo, RhW) containing bridging 1,2-dicarba-closo-dodecaborane-1,2-dichalocogenolato ligands

The 16-electron half-sandwich rhodium complex [Cp*Rh{E2C2(B10H10)}] [Cp* = eta5-C5Me5, E = S (1a), Se (1b)] [Cp*Rh{E2C2(B10H10)} = eta5-pentamethylcyclopentadienyl[1,2-dicarba-closo-dodecaborane(12)-dichalcogenolato]rhodium] reacted with Mo(CO)3(py)3 in the presence of BF3.Et2O in THF solution to afford the {Cp*Rh[E2C2(B10H10)]}2Mo(CO)2 (E = S (3a); Se (3b)), {Cp*Rh[S2C2(B10H10)]}{Mo(CO)2[S2C2(B10H10)]} (4). The voluminous di-tert-butyl substituted Cp half-sandwich rhodium complex [Cp'Rh{E2C2(B10H10)}] [E = S (2a), Se (2b)] [CpRh{E2C2(B10H10)} = eta5-(1,3-di(tert-butyl)cyclopentadienyl-[1,2-dicarba-closo-dodecaborane(12)-dichalcogenolato]rhodium) reacted with W(CO)3(py)3 in the presence of BF3.Et2O in THF solution to give the {Cp'Rh[S2C2(B10H10)]}{W(CO)2[S2C2(B10H10)]} (5) and {Cp'Rh[Se2C2(B10H10)]}(mu-CO)[W(CO)3] (6), respectively. The complexes have been fully characterized by IR and NMR spectroscopy as well as by elemental analyses. The X-ray crystal structures of the complexes 3-6 are reported.     

Silylene hydride complexes of molybdenum with silicon-hydrogen interactions: neutron structure of (eta(5)-C(5)Me(5))(Me(2)PCH(2)CH(2)PMe(2))Mo(H)(SiEt(2))

Reduction of CpMoCl(4) with 3.1 equiv of Na/Hg amalgam (1.0% w/w) in the presence of 1 equiv of dmpe and 1 equiv of trimethylphosphine afforded the molybdenum(II) chloride complex Cp(dmpe)(PMe(3))MoCl (1) (Cp = 1,2,3,4,5-pentamethylcyclopentadienyl, dmpe = 1,2-bis(dimethylphosphino)ethane). Alkylation of 1 with PhCH(2)MgCl proceeded in high yield to liberate PMe(3) and give the 18-electron pi-benzyl complex Cp(dmpe)Mo(eta(3)-CH(2)Ph) (2). Variable temperature NMR experiments provided evidence that 2 is in equilibrium with its 16-electron eta(1)-benzyl isomer [Cp(dmpe)Mo(eta(1)-CH(2)Ph)]. This was further supported by reaction of 2 with CO to yield the carbonyl benzyl complex Cp(dmpe)(CO)Mo(eta(1)-CH(2)Ph) (3). Complex 2 was found to react with disubstituted silanes H(2)SiRR' (RR' = Me(2), Et(2), MePh, and Ph(2)) to form toluene and the silylene complexes Cp(dmpe)Mo(H)(SiRR') (4a: RR' = Me(2); 4b: RR' = Et(2); 4c: RR' = MePh; 4d: RR' = Ph(2)). Reactions of 2 with monosubstituted silanes H(3)SiR (R = Ph, Mes, Mes = 2,4,6-trimethylphenyl) produced rare examples of hydrosilylene complexes Cp(dmpe)Mo(H)Si(H)R (5a: R = Ph; 5b: R = Mes; 5c: R = CH(2)Ph). Reactivity of complexes 4a-c and 5a-d is dominated by 1,2-hydride migration from metal to silicon, and these complexes possess H.Si bonding interactions, as supported by spectroscopic and structural data. For example, the J(HSi) coupling constants in these species range in value from 30 to 48 Hz and are larger than would be expected in the absence of H.Si bonding. A neutron diffraction study on a single crystal of diethylsilylene complex 4b unequivocally determined the hydride ligand to be in a bridging position across the molybdenum-silicon bond (Mo-H 1.85(1) A, Si-H 1.68(1) A). The synthesis and reactivity properties of these complexes are described in detail.     

Reactions of the tetrahedral clusters [MCo(3)(CO)(12)](-) (M = Ru, Fe) with functional mono- and diynes

The tetrahedral cluster [RuCo(3)(CO)(12)](-) reacts with various alkynes, including the new PhCtbd1;CC(O)NHCH(2)Ctbd1;CH (L(1)()), to afford the butterfly clusters [RuCo(3)(CO)(10)(micro(4)-eta(2)-RC(2)R')](-) (1, R = R' = C(O)OMe; 2, R = H, R' = Ph; 3, R = H, R' = MeC=CH(2); 4, R = H, R' = CH(2)OCH(2)Ctbd1;CH; 5, R = H, R' = CH(2)NHC(O)Ctbd1;CPh), in which the ruthenium atom occupies a hinge position and the alkyne is coordinated in a micro(4)-eta(2) fashion. Reaction of the anions 1-3 with [Cu(NCMe)(4)]BF(4) led to selective loss of the 12e fragment Co(CO)(-) to form [RuCo(2)(CO)(9)(micro(3)-eta(2)-RC(2)R')] (6, R = R' = C(O)OMe; 7, R = H, R' = Ph; 8, R = H, R' = MeC=CH(2)). To prepare functionalized RuCo(3) or FeCo(3) clusters that could be subsequently condensed with a silica matrix via the sol-gel method, we reacted [MCo(3)(CO)(12)](-) (M = Ru, Fe) with the alkyne PhCtbd1;CC(O)NH(CH(2))(3)Si(OMe)(3)(L(2)()) and obtained the butterfly clusters [MCo(3)(CO)(10)(micro(4)-eta(2)-PhC(2)C(O)NH(CH(2))(3)Si(OMe)(3))](-) 9 and 10, respectively. Air-stable [RuCo(3)(CO)(10)(micro(4)-eta(2)-Me(3)SiC(2)Ctbd1;CSiMe(3))](-) (11) was obtained from 1,4-bis(trimethylsilyl)butadiyne and reacted with [Cu(NCMe)(4)]BF(4) to give [RuCo(2)(CO)(9)(micro(3)-eta(2)-HC(2)Ctbd1;CSiMe(3))] (12), owing to partial ligand proto-desilylation, and not the expected [RuCo(2)(CO)(9)(micro(3)-eta(2)-Me(3)SiC(2)Ctbd1;CSiMe(3))]. Reaction of 11 with [NO]BF(4) afforded, in addition to 12, [RuCo(3)(CO)(9)(NO)(micro(4)-eta(2)-Me(3)SiC(2)Ctbd1;CSiMe(3))] (13) owing to selective CO substitution on a wing-tip cobalt atom with NO. The thermal reaction of 11 with [AuCl(PPh(3))] led to replacement of a CO on Ru by the PPh(3) originating from [AuCl(PPh(3))] and afforded [RuCo(3)(CO)(9)(PPh(3))(micro(4)-eta(2)-Me(3)SiC(2)Ctbd1;CSiMe(3))](-) (14), also obtained directly by reaction of 11 with one equivalent of PPh(3). Proto-desilylation of 11 using TBAF/THF-H(2)O afforded [RuCo(3)(CO)(10)(micro(4)-eta(2)-Me(3)SiC(2)Ctbd1;CH)](-) (15) which, by Sonogashira coupling with 1,4-diiodobenzene, yielded the dicluster complex [[RuCo(3)(CO)(10)(micro(4)-eta(2)-Me(3)SiC(2)Ctbd1;C)]](2)C(6)H(4)](2)(-) (16). The crystal structures of NEt(4).3a, NEt(4).4a, 6, NEt(4).11b, NEt(4).14, and [N(n-Bu)(4)].15a have been determined by X-ray diffraction. Preliminary results indicate the potential of silica-tethered alkyne mixed-metal clusters, obtained by the sol-gel method, as precursors to bimetallic particles.     

Synthesis,characterization, and solution redox properties of (trimpsi)M(CO)(2)(NO) complexes [M = V,Nb, Ta; trimpsi = (t)BuSi(CH(2)PMe(2))(3)

Treatment of [Et(4)N][M(CO)(6)] (M = Nb, Ta) with I(2) in DME at -78 degrees C produces solutions of the bimetallic anions [M(2micro-I)(3)(CO)(8)](-). Addition of the tripodal phosphine (t)BuSi(CH(2)PMe(2))(3) (trimpsi) followed by refluxing affords (trimpsi)M(CO)(3)I [M = Nb (1), Ta (2)], which are isolable in good yields as air-stable, orange-red microcrystalline solids. Reduction of these complexes with 2 equiv of Na/Hg, followed by treatment with Diazald in THF, results in the formation of (trimpsi)M(CO)(2)(NO) [M = Nb (3), Ta (4)] in high isolated yields. The congeneric vanadium complex, (trimpsi)V(CO)(2)(NO) (5), can be prepared by reacting [Et(4)N][V(CO)(6)] with [NO][BF(4)] in CH(2)Cl(2) to form V(CO)(5)(NO). These solutions are treated with 1 equiv of trimpsi to obtain (eta(2)-trimpsi)V(CO)(3)(NO). Refluxing orange THF solutions of this material affords 5 in moderate yields. Reaction of (trimpsi)VCl(3)(THF) (6) with 4 equiv of sodium naphthalenide in THF in the presence of excess CO provides [Et(4)N][(trimpsi)V(CO)(3)] (7), (trimpsi)V(CO)(3)H, and [(trimpsi)V(micro-Cl)(3)V(trimpsi)][(eta(2)-trimpsi)V(CO)(4)].3THF ([8][9].3THF). All new complexes have been characterized by conventional spectroscopic methods, and the solid-state molecular structures of 2.(1)/(2)THF, 3-5, and [8][9].3THF have been established by X-ray diffraction analyses. The solution redox properties of 3-5 have also been investigated by cyclic voltammetry. Cyclic voltammograms of 3 and 4 both exhibit an irreversible oxidation feature in CH(2)Cl(2) (E(p,a) = -0.71 V at 0.5 V/s for 3, while E(p,a) = -0.55 V at 0.5 V/s for 4), while cyclic voltammograms of 5 in CH(2)Cl(2) show a reversible oxidation feature (E(1/2) = -0.74 V) followed by an irreversible feature (0.61 V at 0.5 V/s). The reversible feature corresponds to the formation of the 17e cation [(trimpsi)V(CO)(2)(NO)](+) ([5](+)()), and the irreversible feature likely involves the oxidation of [5](+)() to an unstable 16e dication. Treatment of 5 with [Cp(2)Fe][BF(4)] in CH(2)Cl(2) generates [5][BF(4)], which slowly decomposes once formed. Nevertheless, [5][BF(4)] has been characterized by IR and ESR spectroscopies.     

A study of structural and bonding variations in the homologous series [Mo(2)(CN)(6)(dppm)(2)](n-) (n = 2, 1, 0)

Reaction of Mo(2)Cl(4)(dppm)(2) (dppm = bis(diphenylphosphino)methane) with 6 equiv of [n-Bu(4)N][CN] or [Et(4)N][CN] in dichloromethane yields [n-Bu(4)N](2)[Mo(2)(CN)(6)(dppm)(2)] (1) and [Et(4)N](2)[Mo(2)(CN)(6)(dppm)(2)] (2), respectively. The corresponding one- and two-electron oxidation products [n-Bu(4)N][Mo(2)(CN)(6)(dppm)(2)] (3) and Mo(2)(CN)(6)(dppm)(2) (4)were prepared by reactions of 1 with the oxidant NOBF(4). Single-crystal X-ray structures of 2.2CH(3)CN, 3.2CH(3)CN.2H(2)O, and 4.2CH(3)NO(2) were performed, and the results confirmed that all three complexes contain identical ligand sets with trans dppm ligands bisecting the Mo(2)(mu-CN)(2)(CN)(4) equatorial plane. The binding of the bridging cyanide ligands is affected by the oxidation state of the dimolybdenum core as evidenced by an increase in side-on pi-bonding overlap of the mu-CN in going from 1 to 4. The greater extent of pi-donation into Mo orbitals is accompanied by a lengthening of the Mo-Mo distance (2.736(1) A in Mo(2)(II,II) (2), 2.830(1) A in Mo(2)(II,III) (3), and 2.936(1) A in Mo(2)(III,III) (4)). A computational study of the closed-shell members of this homologous series, [Mo(2)(CN)(6)(dppm)(2)](n)() (n = 2-, 0), indicates that the more pronounced side-on pi-donation evident in the X-ray structure of 4 leads to significant destabilization of the delta orbital and marginal stabilization of the delta() orbitals with respect to nearly degenerate delta and delta orbitals in the parent compound, 2. The loss of delta contributions combined with the reduced orbital overlap due to higher charges on molybdenum centers in oxidized complexes 3 and 4 is responsible for the observed increase in the length of the Mo-Mo bond.     

Insertion reactions of trans-Mo(dmpe)2(H)(NO) with imines

The insertion chemistry of the hydride complex trans-Mo(dmpe)(2)(H)(NO) (1) (dmpe = bis(dimethylphosphino)ethane) with imines has been investigated. It was found that disubstituted aromatic imines RCH[double bond]NR' (R, R' = Ar) insert into the Mo-H bond of 1, while a series of various mono- and other disubstituted imines do not react. The insertion products trans-Mo(dmpe)(2)(NO)[NR'(CH(2)R)] (R = R' = Ph (2); R = Cp(2)Fe, R' = Ph (3); R = Ph, R' = Cp(2)Fe (4); R = 1-naphthyl, R' = Ph (5)) have been isolated and fully characterized by elemental analysis, IR and NMR spectroscopy, and mass spectrometry. The imine PhCH[double bond]NC(10)H(7) (C(10)H(7) = 1-naphthyl) reacted with 1 establishing an equilibrium to produce the nonisolable complex trans-Mo(dmpe)(2)(NO)[NC(10)H(7)(CH(2)Ph)] (6). The equilibrium constant for this reaction has been derived from VT-NMR measurements, and the Delta H and Delta S values of this reaction were calculated to be -48.8 +/- 0.4 kJ.mol(-1) and -33 +/- 1 J.K(-1).mol(-1) reflecting a mild exothermic process and its associative nature. Single-crystal X-ray diffraction analyses were carried out on 2-5.     

Dihydrogen complexes of rhodium: [RhH2(H2)x (PR3)2]+ (R = Cy, iPr; x = 1, 2)

Addition of H2 (4 atm at 298 K) to [Rh(nbd)(PR3)2][BAr(F)4] [R = Cy, iPr] affords Rh(III) dihydride/dihydrogen complexes. For R = Cy, complex 1a results, which has been shown by low-temperature NMR experiments to be the bis-dihydrogen/bis-hydride complex [Rh(H)2(eta2-H2)2(PCy3)2][BAr(F)4]. An X-ray diffraction study on 1a confirmed the {Rh(PCy3)2} core structure, but due to a poor data set, the hydrogen ligands were not located. DFT calculations at the B3LYP/DZVP level support the formulation as a Rh(III) dihydride/dihydrogen complex with cis hydride ligands. For R = iPr, the equivalent species, [Rh(H)2(eta2-H2)2(P iPr3)2][BAr(F)4] 2a, is formed, along with another complex that was spectroscopically identified as the mono-dihydrogen, bis-hydride solvent complex [Rh(H)2(eta2-H2)(CD2Cl2)(P iPr3)2][BAr(F)4] 2b. The analogous complex with PCy3 ligands, [Rh(H)2(eta2-H2)(CD2Cl2)(PCy3)2][BAr(F)4] 1b, can be observed by reducing the H2 pressure to 2 atm (at 298 K). Under vacuum, the dihydrogen ligands are lost in these complexes to form the spectroscopically characterized species, tentatively identified as the bis hydrides [Rh(H)2(L)2(PR3)2][BAr(F)4] (1c R = Cy; 2c R = iPr; L = CD2Cl2 or agostic interaction). Exposure of 1c or 2c to a H2 atmosphere regenerates the dihydrogen/bis-hydride complexes, while adding acetonitrile affords the bis-hydride MeCN adduct complexes [Rh(H)2(NCMe)2(PR3)2][BAr(F)4]. The dihydrogen complexes lose [HPR3][BAr(F)4] at or just above ambient temperature, suggested to be by heterolytic splitting of coordinated H2, to ultimately afford the dicationic cluster compounds of the type [Rh6(PR3)6(mu-H)12][BAr(F)4]2 in moderate yield.     

Iron complexes for the catalytic transfer hydrogenation of acetophenone: steric and electronic effects imposed by alkyl substituents at phosphorus

A series of iron(II) complexes, trans-[Fe(NCMe)(2)(PR(2)CH(2)CH═NCH(2)CH(2)N═CHCH(2)PR(2))][BPh(4)](2) (5, R = Cy; 7, R = iPr; 9, R = Et) were prepared via the template synthesis in one-pot involving air-stable phosphonium dimers, [cyclo-(-PR(2)CH(2)CH(OH)-)(2)](Br)(2) (4, R = Cy; 6, R = iPr; 8, R = Et), KOtBu, [Fe(H(2)O)(6)][BF(4)](2) and ethylenediamine in acetonitrile. In the synthesis of 9, a methanol/acetonitrile solvent mixture was required; otherwise an intermediate iron bis(tridentate) complex, [Fe(PEt(2)CH(2)CH═NCH(2)CH(2)NH(2))(2)](2+), formed as determined by electrospray ionization mass spectrometry (ESI-MS). The crude iron(II) complexes from a template synthesis with ethylenediamine or (S,S)-1,2-diphenylethylenediamine are stirred in acetone under a CO atmosphere (～2 atm) overnight to displace a NCMe ligand; however, in addition to this, bromide displaces an NCMe ligand as well to form a new class of the iron complexes trans-[Fe(CO)(Br)(PR(2)CH(2)CH═NCHR'CHR'N═CHCH(2)PR(2))](+) (10 R = Cy, R' = H; (S,S)-11, R = Cy, R' = Ph; 12, R = iPr, R' = H; (S,S)-13, R = iPr, R' = Ph; 14, R = Et, R' = H; (S,S)-15, R = Et, R' = Ph). These complexes were isolated in moderate yields (55-84%) as tetraphenylborate salts. Complexes 10-15 were tested for the catalytic transfer hydrogenation of acetophenone in basic iso-propanol at 25 and 50 °C. The complexes 10-13 (where R = Cy or iPr) were inactive while the complexes 14 and (S,S)-15 (where R = Et) were active at 25 °C but had better activity at 50 °C. Complex (S,S)-15 was higher in activity than complex 14, achieving turnover frequencies as high as 4100 h(-1), conversions of acetophenone to (R)-1-phenylethanol as high as 80% and an enantiomeric excess (e.e.) of 50% in the product. As catalysis progressed, the e.e. diminished to as low as 26%.     

Photochemical reactions of (eta 5-cyclopentadienyl)bis(t-butylacrylate) rhodium with silanes: dynamics of isomer interconversion via Rh(eta 2-silane) species

The compound CpRh(C(2)H(3)CO(2)(t)Bu)(2) 1 has been synthesised as a mixture of two pairs of interconverting isomers which differ in the relative orientations of the alkene substituents. The four isomers have been fully characterised by NMR spectroscopy. When complex 1 is photolysed in the presence of a silane, HSiR(2)R'R(2)R'= Et(3), Me(3), HEt(2), (OMe)(3) and Me(2)Cl] the corresponding Si-H oxidative addition products CpRh(SiR(2)R')(H)(C(2)H(3)CO(2)(t)Bu) and CpRh(H)(2)(SiR(2)R')(2) are formed. The Rh(III) complexes CpRh(SiR(2)R')(H)(C(2)H(3)CO(2)(t)Bu) exist in two isomeric forms of comparable energy which interconvert in an intramolecular process that does not involve a reversible [1,3] hydride or [1,3] silyl migration. The hydride (1)H NMR resonances for these species consequently broaden before coalescing into a single peak. For R(2)R'= Et(3), the activation parameters for interchange from the major to minor isomer were Delta H++= 60.2 +/- 2 kJ mol(-1) and Delta S++= 8 +/- 9 J mol(-1) K(-1), while for R(2)R'= Me(3) and Et(2)H, Delta H++= 61.5 +/- 1 kJ mol(-1), Delta S++= 6 +/- 5 J mol(-1) K(-1), and Delta H++= 61.8 +/- 3 kJ mol(-1), Delta S++= 12 +/- 9 J mol(-1) K(-1) respectively for conversion from the major isomer to the minor. For these complexes an eta(2)-Rh-H-Si transition state or intermediate is consistent with the evidence. When R(2)R'=(OMe)(3) and Me(2)Cl the change in appearance of the hydride resonances is more complex, with the activation parameters for interchange from the major to minor isomer for the former species being Delta H++= 78.3 +/- 2 kJ mol(-1) and Delta S++= 30 +/- 7 J mol(-1) K(-1) while for Me(2)Cl the barrier proved too high to measure before decomposition occurred. The complex spectral changes could be simulated when a discrete eta(2)-Rh-H-Si intermediate was involved in the isomer interconversion process and hence silane rotation in all these systems is proposed to involve two isomers of CpRh(eta(2)-HSiR(2)R')(C(2)H(3)CO(2)(t)Bu).     

The synthesis, characterisation and reactivity of 2-phosphanylethylcyclopentadienyl complexes of cobalt, rhodium and iridium

2-Phosphanylethylcyclopentadienyl lithium compounds, Li[C(5)R'(4)(CH(2))(2)PR(2)] (R = Et, R' = H or Me, R = Ph, R' = Me), have been prepared from the reaction of spirohydrocarbons C(5)R'(4)(C(2)H(4)) with LiPR(2). C(5)Et(4)HSiMe(2)CH(2)PMe(2), was prepared from reaction of Li[C(5)Et(4)] with Me(2)SiCl(2) followed by Me(2)PCH(2)Li. The lithium salts were reacted with [RhCl(CO)(2)](2), [IrCl(CO)(3)] or [Co(2)(CO)(8)] to give [M(C(5)R'(4)(CH(2))(2)PR(2))(CO)] (M = Rh, R = Et, R' = H or Me, R = Ph, R' = Me; M = Ir or Co, R = Et, R' = Me), which have been fully characterised, in many cases crystallographically as monomers with coordination of the phosphorus atom and the cyclopentadienyl ring. The values of nu(CO) for these complexes are usually lower than those for the analogous complexes without the bridge between the cyclopentadienyl ring and the phosphine, the exception being [Rh(Cp'(CH(2))(2)PEt(2))(CO)] (Cp' = C(5)Me(4)), the most electron rich of the complexes. [Rh(C(5)Et(4)SiMe(2)CH(2)PMe(2))(CO)] may be a dimer. [Co(2)(CO)(8)] reacts with C(5)H(5)(CH(2))(2)PEt(2) or C(5)Et(4)HSiMe(2)CH(2)PMe(2) (L) to give binuclear complexes of the form [Co(2)(CO)(6)L(2)] with almost linear PCoCoP skeletons. [Rh(Cp'(CH(2))(2)PEt(2))(CO)] and [Rh(Cp'(CH(2))(2)PPh(2))(CO)] are active for methanol carbonylation at 150 degrees C and 27 bar CO, with the rate using [Rh(Cp'(CH(2))(2)PPh(2))(CO)] (0.81 mol dm(-3) h(-1)) being higher than that for [RhI(2)(CO)(2)](-) (0.64 mol dm(-3) h(-1)). The most electron rich complex, [Rh(Cp'(CH(2))(2)PEt(2))(CO)] (0.38 mol dm(-3) h(-1)) gave a comparable rate to [Cp*Rh(PEt(3))(CO)] (0.30 mol dm(-3) h(-1)), which was unstable towards oxidation of the phosphine. [Rh(Cp'(CH(2))(2)PEt(2))I(2)], which is inactive for methanol carbonylation, was isolated after the methanol carbonylation reaction using [Rh(Cp'(CH(2))(2)PEt(2))(CO)]. Neither of [M(Cp'(CH(2))(2)PEt(2))(CO)] (M = Co or Ir) was active for methanol carbonylation under these conditions, nor under many other conditions investigated, except that [Ir(Cp'(CH(2))(2)PEt(2))(CO)] showed some activity at higher temperature (190 degrees C), probably as a result of degradation to [IrI(2)(CO)(2)](-). [M(Cp'(CH(2))(2)PEt(2))(CO)] react with MeI to give [M(Cp'(CH(2))(2)PEt(2))(C(O)Me)I] (M = Co or Rh) or [Ir(Cp'(CH(2))(2)PEt(2))Me(CO)]I. The rates of oxidative addition of MeI to [Rh(C(5)H(4)(CH(2))(2)PEt(2))(CO)] and [Rh(Cp'(CH(2))(2)PPh(2))(CO)] are 62 and 1770 times faster than to [Cp*Rh(CO)(2)]. Methyl migration is slower, however. High pressure NMR studies show that [Co(Cp'(CH(2))(2)PEt(2))(CO)] and [Cp*Rh(PEt(3))(CO)] are unstable towards phosphine oxidation and/or quaternisation under methanol carbonylation conditions, but that [Rh(Cp'(CH(2))(2)PEt(2))(CO)] does not exhibit phosphine degradation, eventually producing inactive [Rh(Cp'(CH(2))(2)PEt(2))I(2)] at least under conditions of poor gas mixing. The observation of [Rh(Cp'(CH(2))(2)PEt(2))(C(O)Me)I] under methanol carbonylation conditions suggests that the rhodium centre has become so electron rich that reductive elimination of ethanoyl iodide has become rate determining for methanol carbonylation. In addition to the high electron density at rhodium.     

Novel metal-to-metal silyl-migration reactions in heterometallic complexes

An unprecedented, intramolecular metal-to-metal silyl ligand migration reaction has been discovered in a series of phosphido-bridged iron-platinum complexes and which may be triggered by an external nucleophile. Thus, reaction of solutions of [(OC)3-(R1/3Si)Fe(mu-PR2R3)Pt(1,5-COD) (1a R1 = OMe, R2 = 3 = Ph; 1b R1 = OMe, R2 = R3 = Cy; 1c R1 = Ph, R2 = R3 = Ph; 1d R1 = Ph, R2 = R3 = Cy; 1e R1 = Ph, R1 = H, R3 = Ph) in CH2Cl2 with CO rapidly afforded the corresponding complexes [(OC)4Fe(mu-PR2R3)Pt(SiR1/3)-(CO)] (2a-e) in which the silyl ligand has migrated from Fe to Pt, while two CO ligands have been ligated, one on each metal. When 1a or 1c was slowly treated with two equivalents of tBuNC at low temperature, quantitative displacement of the COD ligand was accompagnied by silyl migration from Fe to Pt and coordination of an isonitrile ligand to Fe and to Pt to give [(OC)3-(tBuNC)Fe(mu-PPh2)Pt[Si(OMe)3](CNtBu)] (3a) and [(OC)3(tBuNC)-Fe(mu-PPh2)Pt[SiPh3](CNtBu)] (3c). Reaction of 2a with one equivalent of tBuNC selectively led to substitution of the Pt-bound CO to give [(OC)4-Fe(mu-PCy2)Pt[Si(OMe)3](CNtBu)] (4b), which reacted with a second equivalent of tBuNC to give [(OC)4Fe(mu-PCy2)-Pt[Si(OMe)3](CNtBu)2] (5b) in which the metal-metal bond has been cleaved. Opening of the Fe-Pt bond was also observed upon reaction of 3a with tBuNC to give [(OC)3(tBuNC)-Fe(mu-PPh2)Pt[Si(OMe)3](CNtBu)2] (6). The silyl ligand migrates from Fe, in which it is trans to mu-PR2R3 in all the metal-metal-bonded complexes, to a position cis to the phosphido bridge on Pt. However, in 5a,b and 6 with no metal-metal bond, the Pt-bound silyl ligand is trans to the phosphido bridge. The intramolecular nature of the silyl migration, which may be formally viewed as a redox reaction, was established by a cross-over experiment consisting of the reaction of 1a and 1d with CO; this yielded exclusively 2a and 2d. The course of the silyl-migration reaction was found to depend a) on the steric properties of the -SiR1/3 ligand, and for a given mu-PR2R3 bridge (R2 = R3 = Ph), the migration rate decreases in the sequence Si(OMe)3> SiMe2Ph> SiMePh2>SiPh3; b) on the phosphido bridge and for a given silyl ligand (R1 = OMe), the migration rate decreases in the order mu-PPh2 > mu-PHCy; c) on the external nucleophile since reaction of 1c with two equivalents of P(OMe)3, P(OPh)3 or Ph2PCH2C(O)Ph led solely to displacement of the COD ligand with formation of 11a-c, respectively, whereas reaction with two equivalents of tBuNC gave the product of silyl migration 3c. Reaction of [(OC)3-[(MeO)3Si]Fe(mu-PPh2)Pt(PPh3)2] (7a) with tBuNC (even in slight excess) occurred stereoselectively with replacement of the PPh3 ligand trans to mu-PPh2, whereas reaction with CO led first to [(OC)3((MeO)3Si)Fe(mu-PPh2)Pt(CO)-(PPh3)] (8a), which then isomerized to the migration product [(OC)4Fe(mu-PPh2)Pt[Si(OMe)3](PPh3)] (9a). Most complexes were characterized by elemental analysis, IR and 1H, 31P, 13C, and 29Si NMR spectroscopy, and in five cases by X-ray diffraction.     

Aurophilic self-assembly of a Mo4Au2 phosphinidene complex with an unprecedented H-shaped planar metal core

The isomers [Mo2Cp2(mu-kappa(1):kappa(1),eta(6)-PR*)(CO)2] (1) and [Mo2Cp(mu-kappa(1):kappa(1),eta(5)-PC5H4)(CO)2(eta(6)-HR*)] (2) (Cp = eta(5)-C5H5; R* = 2,4,6-C6H2(t)Bu3) react with [AuCl(THT)] and with the cation [Au(THT)2](+) (THT = tetrahydrothiophene) to give phosphinidene-bridged Mo2Au complexes resulting from the addition of an AuCl or Au(THT)(+) electrophile to their multiple P-Mo bonds. Removal of the Cl(-) or THT ligand from these derivatives causes a dimerization of the trinuclear structures to give the cationic derivative [{AuMo2Cp(mu3-kappa(1):kappa(1):kappa(1),eta(5)-PC5H4)(CO)2(eta(6)-HR*)}2](2+), which displays a novel H-shaped metal core held by strong Mo-Au dative bonds [2.768(1) A] and an aurophilic interaction [Au-Au = 3.022(1) A].