Increased reactivity of the *Cr(CO)3(C5Me5) radical with thiones versus thiols: a theoretical and experimental investigation

2-pyridinethione (2-mercaptopyridine, H-2mp) undergoes rapid oxidative addition with 2 mol of the 17-electron organometallic radical *Cr(CO)3Cp (where Cp*=C5Me5), yielding hydride H-Cr(CO)3Cp* and thiolate (eta1-2mp)Cr(CO)3Cp*. In a slower secondary reaction, (eta1-2mp)Cr(CO)3Cp* loses CO generating the N,S-chelate complex (eta2-2mp)Cr(CO)2Cp* for which the crystal structure is reported. The rate of 2-pyridine thione oxidative addition with *Cr(CO)3Cp* (abbreviated *Cr) in toluene best fits rate=kobs[H-2mp][*Cr]; kobs(288 K)=22 +/- 4 M(-1) s(-1); DeltaH++=4 +/- 1 kcal/mol; DeltaS++=- 40 +/- 5 cal/mol K. The rate of reaction is the same under CO or Ar, and the reaction of deuterated 2-pyridine thione (D-2mp) shows a negligible (inverse) kinetic isotope effect (kD/kH=1.06 +/- 0.10). The rate of decarbonylation of (eta1-2mp)Cr(CO)3Cp* forming (eta2-2mp)Cr(CO)2Cp* obeys simple first-order kinetics with kobs (288 K)=3.1x10(-4) s(-1), DeltaH++=23 +/- 1 kcal/mol, and DeltaS++=+ 5.0 +/- 2 cal/mol K. Reaction of 4-pyridine thione (4-mercaptopyridine, H-4mp) with *Cr(CO)3Cp* in THF and CH2Cl2 also follows second-order kinetics and is approximately 2-5 times faster than H-2mp in the same solvents. The relatively rapid nature of the thione versus thiol reactions is attributed to differences in the proposed 19-electron intermediate complexes, [*(S=C5H4N-H)Cr(CO)3Cp*] versus [*(H-S-C6H5)Cr(CO)3Cp*]. In comparison, reactions of pyridyl disulfides occur by a mechanism similar to that followed by aryl disulfides involving direct attack of the sulfur-sulfur bond by the metal radical. Calorimetric data indicate Cr-SR bond strengths for aryl and pyridyl derivatives are similar. The experimental conclusions are supported by B3LYP/6-311+G(3df,2p) calculations, which also provide additional insight into the reaction pathways open to the thione/thiol tautomers. For example, the reaction between H* radical and the 2-pyridine thione S atom yielding a thionyl radical is exothermic by approximately 30 kcal/mol. In contrast, the thiuranyl radical formed from the addition of H* to the 2-pyridine thiol S atom is predicted to be unstable, eliminating either H* or HS* without barrier.     

Parallel modes of C-H bond activation initiated by CpMo(NO)(CH2CMe3)(C6H5) at ambient temperatures

The molybdenum nitrosyl complex Cp*Mo(NO)(CH2CMe3)(C6H5) reacts at room temperature via elimination of neopentane or benzene to form the transient species Cp*Mo(NO)(=CHCMe3) and Cp*Mo(NO)(eta2-C6H4). These reactive intermediates effect the intermolecular activation of hydrocarbon C-H bonds via the reverse of the transformations by which they are generated. Thermolysis of Cp*Mo(NO)(CH2CMe3)(C6H5) in pyridine yields the adducts Cp*Mo(NO)(=CHCMe3)(NC5H5) and Cp*Mo(NO)(eta2-C6H4)(NC5H5), and the benzyne complex has been characterized by X-ray diffraction.     

Role of the transition metal in metallaborane chemistry. Reactivity of (Cp*ReH2)2B4H4 with BH3.thf, CO, and Co2(CO)8

The reaction of Cp*ReCl4, [Cp*ReCl3]2, or [Cp*ReCl2]2 (Cp* = eta 5-C5Me5) with LiBH4 leads to the formation of 7-skeletal-electron-pair (7-sep) (Cp*ReH2)2(B2H3)2 (1) together with Cp*ReH6. Compound 1 is metastable and eliminates H2 at room temperature to generate 6-sep (Cp*ReH2)2B4H4 (2). The reaction of 2 with BH3.thf produces 7-sep (Cp*Re)2B7H7, a hypoelectronic cluster characterized previously. Heating of 2 with 1 atm of CO leads to 6-sep (Cp*ReCO)(Cp*ReH2)B4H4 (3). Both 2 and 3 have the same bicapped Re2B2 tetrahedral cluster core structure. Monitoring the reaction of 2 with CO at room temperature by NMR reveals the formation of a 7-sep, metastable intermediate, (Cp*ReCO)(Cp*ReH2)(B2H3)2 (4), which converts to 3 on heating. An X-ray structure determination reveals two isomeric forms (4-cis and 4-trans) in the crystallographic asymmetric unit which differ in geometry relative to the disposition of the metal ancillary ligands with respect to the Re-Re bond. The presence of these isomers in solution is corroborated by the solution NMR data and the infrared spectrum. In both isomers, the metallaborane core consists of fused B2Re2 tetrahedra sharing the Re2 fragment. On the basis of similarities in electron count and spectroscopic data, 1 also possesses the same bitetrahedral structure. The reaction of 2 with CO2(CO)8 results in the formal replacement of the four rhenium hydrides with a 4-electron CO2(CO)5 fragment, thereby closing the open face in 2 to produce the 6-sep hypoelectronic cluster (Cp*Re)2CO2(CO)5B4H4 (5). These reaction outcomes are compared and contrasted with those previously observed for 5-sep (Cp*Cr2)2B4H8.     

Structural and magnetic studies of the tris(cyclopentadienyl)manganese(II) "paddle-wheel" anions [Cp(3-n)(MeCp)(n)Mn](-) (n=0-3, MeCp=C(5)H(4)CH(3), Cp=C(5)H(5))

The ion-contact complexes [{(eta(5)-Cp)(2)Mn(eta(2):eta(5)-Cp)K}(3)]x0.5 THF (1x0.5 THF) and [{(eta(2)-Cp)(2)(eta(2);eta(5)-MeCp)MnK(thf)}]x2 THF (2x2 THF) and ion-separated complexes [Mg(thf)(6)][(eta(2)-Cp)(3)Mn](2) (3), [Mg(thf)(6)][(eta(2)-Cp)(eta(2)-MeCp)(2)Mn)](2)x0.5 THF (4x0.5 THF), [Mg(thf)(6)][(eta(2)-MeCp)(3)Mn)](2)x0.5 THF (5x0.5 THF) and [Li([12]crown-4)](5)[(eta-Cp)(3)Mn](5) (6) (Cp=C(5)H(5), CpMe=C(5)H(4)CH(3)), have been prepared and structurally characterised. The effects of varying the Cp and CpMe ligands in complexes 1-5 have been probed by variable-temperature magnetic susceptibility measurements and EPR spectroscopic studies.     

Silylenediamido [(CH3)2Si(NTs)2(2-); Ts = p-CH3C6H4SO2] complexes of iridium: synthesis, structures and facile Si-N bond cleavage

The N,N'-bis(sulfonyl)diaminosilane TsdmsinH(2) (TsdmsinH(2) = (CH(3))(2)Si(NHTs)(2), Ts = p-CH(3)C(6)H(4)SO(2)) reacted with [Cp*IrCl(2)](2) (Cp* = eta(5)-C(5)(CH(3))(5)) in the presence of a base to give the coordinatively unsaturated (silylenediamido)iridium complex [Cp*Ir(Tsdmsin)] (2), which was further converted to the 18e adducts [Cp*Ir(Tsdmsin)L] (L = P(C(6)H(5))(3) (3a), P(OC(2)H(5))(3), CO); the reactions of 2 and 3a with water led to the formation of the imido-bridged dinuclear complex [Cp*Ir(micro(2)-NTs)(2)IrCp*] and the bis(amido) complex [Cp*Ir(NHTs)(2){P(C(6)H(5))(3)}], respectively.     

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].     

Syntheses,reactivity, and crystal structures of molybdenum complexes with pyridine-2-thionate (pyS)-containing ligands: crystal structures of [Mo(eta(3)-C(3)H(5))(CO)(2)](2)(mu-eta(1),eta(2)-pyS)(2), exo-[Mo(eta(3)-C(3)H(5))(CO)(eta(2)-pyS)(eta(2)-dppe)], [Mo(CO)(3)(eta(1)-SC(5)H(4)NH)(eta(2)-dppm)], and [Mo(CO)(eta(2)-pyS)(2)(eta(2)-dppm)

The doubly bridged pyridine-2-thionate (pyS) dimolybdenum complex [Mo(eta(3)-C(3)H(5))(CO)(2)](2)(mu-eta(1),eta(2)-pyS)(2) (1) is accessible by the reaction of [Mo(eta(3)-C(3)H(5))(CO)(2)(CH(3)CN)(2)Br] with pySK in methanol at room temperature. Complex 1 reacts with piperidine in acetonitrile to give the complex [Mo(eta(3)-C(3)H(5))(CO)(2)(eta(2)-pyS)(C(5)H(10)NH)] (2). Treatment of 1 with 1,10-phenanthroline (phen) results in the formation of complex [Mo(eta(3)-C(3)H(5))(CO)(2)(eta(1)-pyS)(phen)] (3), in which the pyS ligand is coordinated to Mo through the sulfur atom. Four conformational isomers, endo,exo-complexes [Mo(eta(3)-C(3)H(5))(CO)(eta(2)-pyS)(eta(2)-diphos)] (diphos = dppm, 4a-4d; dppe, 5a-5d), are accessible by the reactions of 1 with dppm and dppe in refluxing acetonitrile. Homonuclear shift-correlated 2-D (31)P((1)H)-(31)P((1)H) NMR experiments of the mixtures 4a-4d have been employed to elucidate the four stereoisomers. The reaction of 4 and pySK or [Mo(CO)(3)(eta(1)-SC(5)H(4)NH)(eta(2)-dppm)] (6) and O(2) affords allyl-displaced seven-coordinate bis(pyridine-2-thionate) complex [Mo(CO)(eta(2)-pyS)(2)(eta(2)-dppm)] (7). All of the complexes are identified by spectroscopic methods, and complexes 1, 5d, 6, and 7 are determined by single-crystal X-ray diffraction. Complexes 1 and 5d crystallize in the orthorhombic space groups Pbcn and Pbca with Z = 4 and 8, respectively, whereas 6 belongs to the monoclinic space group C2/c with Z = 8 and 7 belongs to the triclinic space group Ponemacr; with Z = 2. The cell dimensions are as follows: for 1, a = 8.3128(1) A, b = 16.1704(2) A, c = 16.6140(2) A; for 5d, a = 17.8309(10) A, b = 17.3324(10) A, c = 20.3716(11) A; for 6, a = 18.618(4) A, b = 16.062(2) A, c = 27.456(6) A, beta = 96.31(3) degrees; for 7, a = 9.1660(2) A, b = 12.0854(3) A, c = 15.9478(4) A, alpha = 78.4811(10) degrees, beta = 80.3894(10) degrees, gamma = 68.7089(11) degrees.     

Metallaboranes of the Early Transition Metals: Direct Synthesis and Characterization of [{(eta5-C5Me5)Ta}2BnHm] (n=4, m=10; n=5, m=11), [{(eta5-C5Me5)Ta}2B5H10(C6H4CH3)], and [{(eta5-C5Me5)TaCl}2B5H11

Reaction of [Cp*TaCl4] (Cp*=eta5-C5Me5) with a sixfold excess of LiBH(4)thf followed by BH3thf in toluene at 100 degrees C led to the isolation of hydrogen-rich metallaboranes [(Cp*Ta)2B4H10] (1), [(Cp*Ta)2B5H11] (2), [(Cp*Ta)2B5H10(C6H4CH3)] (3), and [(Cp*TaCl)2B5H11] (4) in modest yield. Compounds 1-3 are air- and moisture-sensitive but 4 is reasonably stable in air. Their structures are predicted by the electron-counting rules to be a bicapped tetrahedron (1), bicapped trigonal bipyramids (2, 3), and a nido structure based on a closo dodecahedron 4. Yellow tantalaborane 1 has a nido geometry with C2v symmetry and is isostructural with [(Cp*M)2B4H8] (M=Cr and Re); whereas 2 and 3 are C3v-symmetric and isostructural with [(Cp*M)2B5H9] (M=Cr, Mo, W) and [(Cp*ReH)2B5Cl5]. The most remarkable feature of 4 is the presence of a hydride ligand bridging the ditantalum center to form a symmetrical tantalaborane cluster with a long Ta--Ta bond (3.22 A). Cluster 4 is a rare example of electronically unsaturated metallaborane containing four TaHB bonds. All these new metallaboranes have been characterized by mass spectrometry, 1H, 11B, and 13C NMR spectroscopy, and elemental analysis, and the structural types were unequivocally established by crystallographic analysis of 1-4.     

Synthesis and crystal structures of (fulvalene)W(2)(SH)(2)(CO)(6), (fulvalene)W(2)(mu-S(2))(CO)(6), and (fulvalene)W(2)(mu-S)(CO)(6): low valent tungsten carbonyl sulfide and disulfide complexes stabilized by the bridging fulvalene ligand

Reaction of FvW(2)(H)(2)(CO)(6) with 2/8S(8) in THF results in rapid and quantitative formation of FvW(2)(SH)(2)(CO)(6). The crystal structure of this complex is reported and shows that the two tungsten-hydrosulfide groups are on opposite faces of the fulvalene ligand in an anti configuration. Nevertheless, treatment of FvW(2)(SH)(2)(CO)(6) (1) with PhN[double bond]NPh produces FvW(2)(mu-S(2))(CO)(6) (2) and Ph(H)NN(H)Ph. The crystal structure of the bridging disulfide, which cocrystallizes with 1 in a 2:1 ratio, is also described. Exposure of 2 equiv of *CrCp*(CO)(3) to 1 effects similar H atom transfers yielding 2 HCrCp*(CO)(3) and 2. Attempts to obtain crystals of the latter from solutions derived from this reaction mixture furnished a third product, FvW(2)(mu-S)(CO)(6) (3), which was analyzed crystallographically. The enthalpy of sulfur atom insertion into FvW(2)(H)(2)(CO)(6), yielding 1, has been measured by solution calorimetry.     

Synthesis and characterization of heterometallic clusters (Ir2Rh, Ir2W, Rh3) Containing 1,2-dicarba-closo-dodecaborane(12)-1,2-dithiolate chelate ligands, [(B10H10)C2S2]2-

The 16-electron half-sandwich complex [Cp*Ir[S2C2(B10H10)]] (Cp* = eta5-C5Me5) (1a) reacts with [[Rh(cod)(mu-Cl)]2] (cod = cycloocta-1,5-diene, C8H12) in different molar ratios to give three products, [[Cp*Ir[S2C2(B10H9)]]Rh(cod)] (2), trans-[[Cp*Ir[S2C2(B10H9)]]Rh[[S2C2(B10H10)]IrCp*]] (3), and [Rh2(cod)2[(mu-SH)(mu-SC)(CH)(B10H10)]] (4). Complex 3 contains an Ir2Rh backbone with two different Ir-Rh bonds (3.003(3) and 2.685(3) angstroms). The dinuclear complex 2 reacts with the mononuclear 16-electron complex 1a to give 3 in refluxing toluene. Reaction of 1a with [W(CO)3(py)3] (py = C5H5N) in the presence of BF3.EtO2 leads to the trinuclear cluster [[Cp*Ir[S2C2(B10H10)]]2W(CO)2] (5) together with [[Cp*Ir(CO)[S2C2(B10H10)]]W(CO)5] (6), and [Cp*Ir(CO)[S2C2(B10H10)]] (7). Analogous reactions of [Cp*Rh[S2C2(B10H10)]] (1 b) with [[Rh(cod)(mu-Cl)]2] were investigated and two complexes cis-[[Cp*Rh[S2C2(B10H10)]]2Rh] (8) and trans-[[Cp*Rh[S2C2(B10H10)]]2Rh] (9) were obtained. In refluxing THF solution, the cisoid 8 is converted in more than 95 % yield to the transoid 9. All new complexes 2-9 were characterized by NMR spectroscopy (1H, 11B NMR) and X-ray diffraction structural analyses are reported for complexes 2-5, 8, and 9.     

Synthetic,structural and binding studies of the 4,6-dimethyldibenzothiophene complex [(eta(5)-C(5)Me(5))Ru(CO)(2)(eta(1)(S)-4,6-Me(2)DBT)]BF(4): toward an understanding of deep hydrodesulfurization

The synthesis of the first completely characterized transition-metal complex containing a sulfur-bound 4,6-dimethyldibenzothiophene (4,6-Me(2)DBT) ligand, [CpRu(CO)(2)(eta(1)(S)-4,6-Me(2)DBT)]BF(4) (1) (Cp = eta(5)-C(5)Me(5)), is reported. X-ray studies of 1 and its 4-methyldibenzothiophene and dibenzothiophene analogues, [CpRu(CO)(2)(eta(1)(S)-4-MeDBT)]BF(4) (2) and [CpRu(CO)(2)(eta(1)(S)-DBT)]BF(4) (3), show that the Ru-S bond distances increase in the order, 3 < 2 < 1. Equilibrium studies on the series of [CpRu(CO)(2)(eta(1)(S)-DBTh)](+) compounds, where DBTh = DBT, 4-MeDBT, 4,6-Me(2)DBT, and 2,8-Me(2)DBT, show that the relative binding strengths of the dibenzothiophene ligands increase in the order 4,6-Me(2)DBT (1) < 4-MeDBT (20.2(1)) < DBT (62.7(6)) < 2,8-Me(2)DBT (223(3)). These results are the first to quantify the steric effect of 4- and 6-methyl groups on the sulfur-coordinating ability of dibenzothiophenes to transition-metal centers. They are also consistent with the proposal that 4- and 6-methyl groups reduce the coordination of dibenzothiophenes to active metal sites on hydrodesulfurization catalysts, which could account for the slow rate of 4-MeDBT and 4,6-Me(2)DBT hydrodesulfurization in petroleum feedstocks.     

Re(eta(5)-C5H5)(CO)3]+ family of 17-electron compounds: monomer/dimer equilibria and other reactions

The anodic electrochemical oxidations of ReCp(CO)3 (1, Cp = eta(5)-C5H5), Re(eta(5)-C5H4NH2)(CO)3 (2), and ReCp*(CO)3 (3, Cp* = eta(5)-C5Me5), have been studied in CH2Cl2 containing [NBu4][TFAB] (TFAB = [B(C6F5)4]-) as supporting electrolyte. One-electron oxidations were observed with E(1/2) = 1.16, 0.79, and 0.91 V vs ferrocene for 1-3, respectively. In each case, rapid dimerization of the radical cation gave the dimer dication, [Re2Cp(gamma)2(CO)6]2+ (where Cp(gamma) represents a generic cyclopentadienyl ligand), which may be itself reduced cathodically back to the original 18-electron neutral complex ReCp(gamma)(CO)3. DFT calculations show that the SOMO of 1+ is highly Re-based and hybridized to point away from the metal, thereby facilitating the dimerization process and other reactions of the Re(II) center. The dimers, isolated in all three cases, have long metal-metal bonds that are unsupported by bridging ligands, the bond lengths being calculated as 3.229 A for [Re2Cp2(CO)6]2+ (1(2)2+) and measured as 3.1097 A for [Re2(C5H4NH2)2(CO)6]2+ (2(2)2+) by X-ray crystallography on [Re2(C5H4NH2)2(CO)6][TFAB]2. The monomer/dimer equilibrium constants are between K(dim) = 10(5) M(-1) and 10(7) M(-1) for these systems, so that partial dissociation of the dimers gives a modest amount of the corresponding monomer that is free to undergo radical cation reactions. The radical 1+ slowly abstracts a chlorine atom from dichloromethane to give the 18-electron complex [ReCp(CO)3Cl]+ as a side product. The radical cation 1+ acts as a powerful one-electron oxidant capable of effectively driving outer-sphere electron-transfer reactions with reagents having potentials of up to 0.9 V vs ferrocene.     

Condensed tantalaborane clusters: synthesis and structures of [(Cp*Ta)2B5H7{Fe(CO)3}2] and [(Cp*Ta)2B5H9{Fe(CO)3}4

The reaction of [(Cp*Ta)(2)B(4)H(9)(μ-BH(4))] (1; Cp* = η(5)-C(5)Me(5)) with [Fe(2)(CO)(9)] in hexane yielded [(Cp*Ta)(2)B(5)H(7){Fe(CO)(3)}(2)] (2) and [(Cp*Ta)(2)B(5)H(9){Fe(CO)(3)}(4)] (3) in moderate yield. Cluster 2 represents the first example of a bicapped pentagonal-bipyramidal metallaborane with a deformed equatorial plane, and 3 can be described as a fused cluster in which two pentagonal-bipyramidal units are fused through a common 3-vertex triangular face. Compounds 2 and 3 have been characterized by mass spectrometry and IR, (1)H, (11)B, and (13)C NMR spectroscopy, and the geometric structures were unequivocally established by crystallographic analysis.     

Insertion of pyridine into an iron-silicon bond: structure of the product Cp*(CO)Fe[eta3(C,C,C)-C5H5NSiMe2NPh2

Heating a toluene solution of Cp*(CO)(C5H5N)FeSiMe2NPh2 led to insertion of pyridine into the iron-silicon bond to form Cp*(CO)Fe[eta3(C,C,C)-C5H5NSiMe2NPh2].     

Characterization and reactions of previously elusive 17-electron cations: electrochemical oxidations of (C(6)H(6))Cr(CO)(3) and (C(5)H(5))Co(CO)(2) in the presence of [B(C(6)F(5))(4)](-)

The electrochemical oxidations of (C6H6)Cr(CO)3, 1, and (C5H5)Co(CO)2, 2, when carried out in CH2Cl2/[NBu4][B(C6F5)4], allow the physical or chemical characterization of the 17-electron cations 1+ and 2+ at room temperature. The generation of 1+ on a synthetic time scale permits an electrochemical "switch" process involving facile substitution of CO by PPh3 as a route to (C6H6)Cr(CO)2PPh3. The radical 2+ undergoes a second-order reaction to give a product assigned as the metal-metal bonded dimer dication [Cp2Co2(CO)4]2+. The new anodic chemistry of these often-studied 18-electron compounds is made possible by increases in the solubility and thermal stability of the cation radicals in media containing the poorly nucleophilic anion [B(C6F5)4]-, TFAB.     

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.     

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.     

Electroswitchable photoluminescence activity: synthesis, spectroscopy, electrochemistry, photophysics, and X-ray crystal and electronic structures of [Re(bpy)(CO)3(C[triple bond]C[bond]C6H4[bond]C[triple bond]C)Fe(C5Me5)(dppe)][PF6](n) (n = 0, 1)

A novel heterobimetallic alkynyl-bridged complex, [Re(bpy)(CO)(3)(C[triple bond]C[bond]C(6)H(4)[bond]C[triple bond]C)Fe(C(5)Me(5))(dppe)], 1, and its oxidized species, [Re(bpy)(CO)(3)(C[triple bond]C[bond]C(6)H(4)[bond]C[triple bond]C)Fe(C(5)Me(5))(dppe)][PF(6)], 2, have been synthesized and their X-ray crystal structures determined. A related vinylidene complex, [Re(bpy)(CO)(3)(C[triple bond]C[bond]C(6)H(4)[bond](H)C[double bond]C)Fe(C(5)Me(5))(dppe)][PF(6)], 3, has also been synthesized and characterized. The cyclic voltammogram of 1 shows a quasireversible reduction couple at -1.49 V (vs SCE), a fully reversible oxidation at -0.19 V, and a quasireversible oxidation at +0.88 V. In accord with the electrochemical results, density-functional theory calculations on the hydrogen-substituted model complex Re(bpy)(CO)(3)(C[triple bond]C[bond]C(6)H(4)[bond]C[triple bond]C)Fe(C(5)H(5))(dHpe) (Cp = C(5)H(5), dHpe = H(2)P[bond](CH(2))(2)[bond]PH(2)) (1-H) show that the LUMO is mainly bipyridine ligand pi* in character while the HOMO is largely iron(II) d orbital in character. The electronic absorption spectrum of 1 shows low-energy absorption at 390 nm with a 420 nm shoulder in CH(2)Cl(2), while that of 2 exhibits less intense low-energy bands at 432 and 474 nm and additional low-energy bands in the NIR at ca. 830, 1389, and 1773 nm. Unlike the related luminescent rhenium(I)-alkynyl complex [Re(bpy)(CO)(3)(C[triple bond]C[bond]C(6)H(4)[bond]C[triple bond]C[bond]H)], 4, complex 1 is found to be nonemissive, and such a phenomenon is attributed to an intramolecular quenching of the emissive d pi(Re) --> pi*(bpy) (3)MLCT state by the low-lying MLCT and LF excited states of the iron moiety. Interestingly, switching on of the luminescence property derived from the d pi(Re) --> pi*(bpy) (3)MLCT state can be demonstrated in the oxidized species 2 and the related vinylidene analogue 3 due to the absence of the quenching pathway.     

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]-.     

Transition metal complexes of the chelating phosphine borane ligand Ph2PCH2Ph2P.BH3

Chromium and ruthenium complexes of the chelating phosphine borane H(3)B.dppm are reported. Addition of H(3)B.dppm to [Cr(CO)(4)(nbd)](nbd = norbornadiene) affords [Cr(CO)(4)(eta1-H(3)B.dppm)] in which the borane is linked to the metal through a single B-H-Cr interaction. Addition of H(3)B.dppm to [CpRu(PR(3))(NCMe)(2)](+)(Cp =eta5)-C(5)H(5)) results in [CpRu(PR(3))(eta1-H(3)B.dppm)][PF(6)](R = Me, OMe) which also show a single B-H-Ru interaction. Reaction with [CpRu(NCMe)(3)](+) only resulted in a mixture of products. In contrast, with [Cp*Ru(NCMe)(3)](+)(Cp*=eta5)-C(5)Me(5)) a single product is isolated in high yield: [Cp*Ru(eta2-H(3)B.dppm)][PF(6)]. This complex shows two B-H-Ru interactions. Reaction with L = PMe(3) or CO breaks one of these and the complexes [Cp*Ru(L)(eta1-H(3)B.dppm)][PF(6)] are formed in good yield. With L = MeCN an equilibrium is established between [Cp*Ru(eta2-H(3)B.dppm)][PF(6)] and the acetonitrile adduct. [Cp*Ru (eta2-H(3)B.dppm)][PF(6)] can be considered as being "operationally unsaturated", effectively acting as a source of 16-electron [Cp*Ru (eta1-H(3)B.dppm)][PF(6)]. All the new compounds (apart from the CO and MeCN adducts) have been characterised by X-ray crystallography. The solid-state structure of H(3)B.dppm is also reported.