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.     

Generation and coupling of [Mn(dmpe)2(C triple bond CR)(C triple bond C)]* radicals producing redox-active C4-bridged rigid-rod complexes

The symmetric d(5) trans-bis-alkynyl complexes [Mn(dmpe)(2)(C triple bond CSiR(3))(2)] (R = Me, 1 a; Et, 1 b; Ph, 1 c) (dmpe = 1,2-bis(dimethylphosphino)ethane) have been prepared by the reaction of [Mn(dmpe)(2)Br(2)] with two equivalents of the corresponding acetylide LiC triple bond CSiR(3). The reactions of species 1 with [Cp(2)Fe][PF(6)] yield the corresponding d(4) complexes [Mn(dmpe)(2)(C triple bond CSiR(3))(2)][PF(6)] (R = Me, 2 a; Et, 2 b; Ph, 2 c). These complexes react with NBu(4)F (TBAF) at -10 degrees C to give the desilylated parent acetylide compound [Mn(dmpe)(2)(C triple bond CH)(2)][PF(6)] (6), which is stable only in solution at below 0 degrees C. The asymmetrically substituted trans-bis-alkynyl complexes [Mn(dmpe)(2)(C triple bond CSiR(3))(C triple bond CH)][PF(6)] (R = Me, 7 a; Et, 7 b) related to 6 have been prepared by the reaction of the vinylidene compounds [Mn(dmpe)(2)(C triple bond CSiR(3))(C=CH(2))] (R = Me, 5 a; Et, 5 b) with two equivalents of [Cp(2)Fe][PF(6)] and one equivalent of quinuclidine. The conversion of [Mn(C(5)H(4)Me)(dmpe)I] with Me(3)SiC triple bond CSnMe(3) and dmpe afforded the trans-iodide-alkynyl d(5) complex [Mn(dmpe)(2)(C triple bond CSiMe(3))I] (9). Complex 9 proved to be unstable with regard to ligand disproportionation reactions and could therefore not be oxidized to a unique Mn(III) product, which prevented its further use in acetylide coupling reactions. Compounds 2 react at room temperature with one equivalent of TBAF to form the mixed-valent species [[Mn(dmpe)(2)(C triple bond CH)](2)(micro-C(4))][PF(6)] (11) by C-C coupling of [Mn(dmpe)(2)(C triple bond CH)(C triple bond C*)] radicals generated by deprotonation of 6. In a similar way, the mixed-valent complex [[Mn(dmpe)(2)(C triple bond CSiMe(3))](2)(micro-C(4))][PF(6)] [12](+) is obtained by the reaction of 7 a with one equivalent of DBU (1,8-diazabicyclo[5.4.0]undec-7-ene). The relatively long-lived radical intermediate [Mn(dmpe)(2)(C triple bond CH)(C triple bond C*)] could be trapped as the Mn(I) complex [Mn(dmpe)(2)(C triple bond CH)(triple bond C-CO(2))] (14) by addition of an excess of TEMPO (2,2,6,6-tetramethyl-1-piperidinyloxy) to the reaction mixtures of species 2 and TBAF. The neutral dinuclear Mn(II)/Mn(II) compounds [[Mn(dmpe)(2)(C triple bond CR(3))](2)(micro-C(4))] (R = H, 11; R = SiMe(3), 12) are produced by the reduction of [11](+) and [12](+), respectively, with [FeCp(C(6)Me(6))]. [11](+) and [12](+) can also be oxidized with [Cp(2)Fe][PF(6)] to produce the dicationic Mn(III)/Mn(III) species [[Mn(dmpe)(2)(C triple bond CR(3))](2)(micro-C(4))][PF(6)](2) (R = H, [11](2+); R = SiMe(3), [12](2+)). Both redox processes are fully reversible. The dinuclear compounds have been characterized by NMR, IR, UV/Vis, and Raman spectroscopies, CV, and magnetic susceptibilities, as well as elemental analyses. X-ray diffraction studies have been performed on complexes 4 b, 7 b, 9, [12](+), [12](2+), and 14.     

Carbon-carbon bond activation of R-CN (R = Me, Ar, iPr, tBu) using a cationic Rh(III) complex

Addition of 1.0 equiv of Ph3SiH to [Cp*(PMe3)Rh(Me)(CH2Cl2)]+BAr'4- (1) resulted in release of methane and quantitative formation of [Cp*(PMe3)Rh(SiPh3)(CH2Cl2)]+BAr'4- (2). Subsequent addition of 1.0 equiv of MeCN to 2 caused immediate displacement of dichloromethane to form the eta1-nitrile adduct [Cp*(PMe3)Rh(SiPh3)(NCMe)]+BAr'4- (3). Upon standing at room-temperature overnight, complex 3 converted quantitatively to another product which has been characterized as the C-C activation product, [Cp*(PMe3)Rh(Me)(CNSiPh3)]+BAr'4- (5). Addition of other nitrile substrates (R-CN, R = Ph, (4-CF3)Ph, (4-MeO)Ph, iPr, tBu) to 2 also resulted in C-C activation of the R-CN bond to form [Cp*(PMe3)Rh(R)(CNSiPh3)]+BAr'4-. Evidence for an eta2-iminoacyl intermediate complex, [Cp*(PMe3)Rh(eta2-C(R)=N(SiPh3)]+BAr'4-, is also presented.     

Transfer hydrogenation processes to mu(3)-alkylidyne groups on the organotitanium oxide [Ti(3)Cp*O(3)

The photochemical treatment of mu(3)-alkylidyne complexes [[TiCp*(mu-O)](3)(mu(3)-CR)] (R=H (1), Me (2), Cp*=eta(5)-C(5)Me(5)) with the amines (2,6-Me(2)C(6)H(3))NH(2), Et(2)NH, and Ph(2)NH and the imine Ph(2)C=NH leads to the partial hydrogenation of the alkylidyne moiety that is supported on the organometallic oxide, [Ti(3)Cp*O(3)], and the formation of new oxoderivatives [[TiCp*(3)(mu-CHR)(R'NR")] (R"=2,6-Me(2)C(6)H(3), R'=H, R=H (3), Me (4); R'=R"=Et, R=H (5), Me (6); R'=R"=Ph, R=H (7), Me (8)) and [[TiCp*(mu-O)](3)(mu-CHR)(N=CPh(2))] (R=H (9), R=Me (10)), respectively. A sequential transfer hydrogenation process occurs when complex 1 is treated with tBuNH(2), which initially gives the mu-methylene [[TiCp*(mu-O)](3)(mu-CH(2))(HNtBu)] (11) complex and finally, the alkyl derivative [[TiCp*(mu-O)](3)(mu-NtBu)Me] (12). Furthermore, irradiation of solutions of the mu(3)-alkylidyne complexes 1 or 2 in the presence of diamines o-C(6)H(4)(NH(2))(2) and H(2)NCH(2)CH(2)NH(2) (en) affords [[TiCp*(mu-O)](3)(mu(3)-eta(2)-NC(6)H(4)NH)] (13) and [[TiCp*(mu-O)](3)(mu(3)-eta(2)-NC(2)H(4)NH)] (14) by either methane or ethane elimination, respectively. In the reaction of 1 with en, an intermediate complex [[TiCp*(mu-O)](3)(mu-CH(2))(NHCH(2)CH(2)NH(2))] (15) is detected by (1)H NMR spectroscopy. Thermal treatment of the complexes 4-10 quantitatively regenerates the starting mu(3)-alkylidyne compounds and the amine R'(2)NH or the imine Ph(2)C=NH; however, heating of solutions of 3 or 4 in [D(6)]benzene or a equimolecular mixture of both at 170 degrees C produces methane, ethane, or both, and the complex [[TiCp*(mu-O)](3)[mu(3)-eta(2)-NC(6)H(3)(Me)CH(2)]] (16). The molecular structure of 8 has been established by single-crystal X-ray analysis.     

Preparation and characterization of diarylphosphazene and diarylphosphinohydrazide complexes of titanium, tungsten and ruthenium and phosphorylketimido complexes of rhenium

Reaction of the proligand Ph2PN(SiMe3)2 (L1) with WCl6 gives the oligomeric phosphazene complex [WCl4(NPPh2)]n, 1 and subsequent reaction with PMe2Ph or NBu4Cl gives [WCl4(NPPh2)(PMe2Ph)] (2) or [WCl5(NPPh2)][NBu4] (3), respectively. DF calculations on [WCl5(NPPh2)][NBu4] show a W=N double bond (1.756 A) and a P-N bond distance of 1.701 A, which combined with the geometry about the P atom suggests, there is no P-N multiple bonding. Reaction of L1 with [ReOX3(PPh3)2] in MeCN (X = Cl or Br) gives [ReX2(NC(CH3)P(O)Ph2)(MeCN)(PPh3)](X = Cl, 4, X = Br, 5) which contains the new phosphorylketimido ligand. It is bound to the rhenium centre with a virtually linear Re-N-C arrangement (Re-N-C angle = 176.6 degrees, when X = Cl) and there is multiple bonding between Re and N (Re-N = 1.809(7) A when X = Cl). The proligand Ph2PNHNMe2(L2H) reacts with [(C5H5)TiCl3] to give [(C5H5)TiCl2(Me2NNPPh2)] (6). An X-ray crystal structure of the complex shows the ligand (L2) is bound by both nitrogen atoms. Reaction of the proligands Ph2PNHNR2[R2 = Me2 (L2H), -(CH2CH2)2NCH3 (L3H), (CH2CH2)2CH2 (L4H)] with [{RuCl(mu-Cl)(eta6-p-MeC6H4iPr)}2] gave [RuCl2(eta6-p-MeC6H4iPr)L] {L = L2H (7), L3H (8), L4H (9)}. The X-ray crystal structures of 7-9 confirmed that the phosphinohydrazine ligand is neutral and bound via the phosphorus only. Reaction of complexes 7-9 with AgBF4 resulted in chloride ion abstraction and the formation of the cationic species [RuCl(6-p-MeC6H4iPr)(L)]+ BF4- {(L = L2H (10), L3H (11), L4H (12)}. Finally, reaction of complex 6 with [{RuCl(mu-Cl)(eta6-p-MeC6H4iPr)}2] gave the binuclear species [(eta6-p-MeC6H4iPr)Cl2Ru(mu2,eta3-Ph2PNNMe2)TiCl2(C5H5)], 13.     

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.     

Silylene extrusion from organosilanes via double geminal Si-H bond activation by a Cp*Ru(kappa2-P,N)+ complex: observation of a key stoichiometric step in the glaser-tilley alkene hydrosilylation mechanism

Treatment of Cp*RuCl(kappa2-P,N-2b) (2b = 2-NMe2-3-PiPr2-indene) with TlSO3CF3 produced the cyclometalated complex [4]+SO3CF3- in 94% isolated yield. Exposure of [4]+X- (X = B(C6F5)4 or SO3CF3) to Ph2SiH2 (10 equiv) or PhSiH3 afforded the corresponding [Cp*(mu-P,N-2b)(H)2Ru=SiRPh]+X- complexes, [5]+X- (R = Ph; X = B(C6F5)4, 82%; X = SO3CF3, 39%) and [6]+X- (R = H; X = B(C6F5)4, 94%; X = SO3CF3, 95%). Notably, these transformations represent the first documented examples of Ru-mediated silylene extrusion via double geminal Si-H bond activation of an organosilane-a key step in the recently proposed Glaser-Tilley (G-T) alkene hydrosilylation mechanism. Treatment of [5]+B(C6F5)4- with KN(SiMe3)2 or [6]+SO3CF3- with NaN(SiMe3)2 afforded the corresponding zwitterionic Cp*(mu-2-NMe2-3-PiPr2-indenide)(H)2Ru=SiRPh complex in 69% (R = Ph, 7) or 86% (R = H, 8) isolated yield. Both [6]+X- and 8 proved unreactive toward 1-hexene and styrene and provided negligible catalytic turnover in the attempted metal-mediated hydrosilylation of these substrates with PhSiH3, thereby providing further empirical evidence for the required intermediacy of base-free Ru=Si species in the G-T mechanism. Isomerization of the P,N-indene ligand backbone in [6]+X-, giving rise to [Cp*(mu-1-PiPr2-2-NMe2-indene)(H)2Ru=SiHPh]+X- ([9]+X-), was observed. In the case of [9]+SO3CF3-, net intramolecular addition of the Ru=Si-H group across the styrene-like C=C unit within the ligand backbone to give 10 (96% isolated yield) was observed. Crystallographic characterization data are provided for [4]+X-, [5]+X-, [6]+X-, 8, and 10.     

Synthesis and characterization of scandium silyl complexes of the type Cp*2ScSiHRR'. sigma-Bond metathesis reactions and catalytic dehydrogenative silation of hydrocarbons

The scandium dihydrosilyl complexes Cp*(2)ScSiH(2)R (R = Mes (4), Trip (5), SiPh(3) (6), Si(SiMe(3))(3) (7); Mes = 2,4,6-Me(3)C(6)H(2), Trip = 2,4,6-(i)()Pr(3)C(6)H(2)) and Cp*(2)ScSiH(SiMe(3))(2) (8) were synthesized by addition of the appropriate hydrosilane to Cp*(2)ScMe (1). Studies of these complexes in the context of hydrocarbon activation led to discovery of catalytic processes for the dehydrogenative silation of hydrocarbons (including methane, isobutene and cyclopropane) with Ph(2)SiH(2) via sigma-bond metathesis.     

Silapropargyl/silaallenyl and silylene acetylide complexes of [Cp(CO)2W]+. Theoretical study of their interesting bonding nature and formation reaction

The geometry and bonding nature of Cp(CO)(2)W(CCH)(SiH(2)) (1) and the reaction leading to the formation of 1 from Cp(CO)(2)W(SiH(2)C triple bond CH)(9) were theoretically investigated with DFT, MP2 to MP4(SDTQ), and CCSD(T) methods, where 9 and 1 were adopted as models of the interesting new complexes reported recently, Cp*(CO)(2)W(Si(Ph)(2)C triple bond C(t)Bu) and Cp*(CO)(2)W(C triple bond C(t)Bu)(SiPh(2)), respectively. Our computational results clearly indicate that 1 involves neither a pure silacyclopropenyl group nor pure silylene and acetylide groups and that the silylene group strongly interacts with both the W center and the acetylide group. Frontier orbitals of 1 resemble those observed in the formation of silacyclopropene from silylene and acetylene. The frontier orbitals, as well as the geometry, indicate that the (CCH)(SiH(2)) moiety of 1 can be understood in terms of an interesting intermediate species trapped by the W center in that formation reaction. Complex 1 is easily formed from 9 through Si-C sigma-bond activation with moderate activation barriers of 15.3, 18.8, and 15.8 kcal/mol, which are the DFT-, MP4(SDTQ)-, and CCSD(T)-calculated values, respectively. This reaction takes place without a change of the oxidation state of the W center. Intermediate 9 is easily formed from Cp(CO)(2)W(Me)(H(3)SiC triple bond CH) via Si-H oxidative addition, followed by C-H reductive elimination. The bonding nature of 9 is also very interesting; the nonbonding pi-orbital of the H(2)SiCCH moiety is essentially the same as that of the propargyl group, but the pi-conjugation between Si and C atoms is very weak in the pi-orbital, unlike that in the propargyl group.     

Cationic hafnium silyl complexes and their enhanced reactivity in sigma-bond metathesis processes with Si-H and C-H bonds

Reaction of the mixed-ring silyl methyl complex CpCp*Hf[Si(SiMe3)3]Me (4) with B(C6F5)3 in bromobenzene-d5 yielded the zwitterionic hafnium silyl complex [CpCpHfSi(SiMe3)3][MeB(C6F5)3] (7), which is stable for at least 12 h in solution. Addition of PhSiH3 to 7 rapidly produced HSi(SiMe3)3, CpCp*HfH(mu-H)B(C6F5)3, and oligomeric silane products. Reactions of CpCp*Hf(SiR3)Me (SiR3 = SitBuPh2, SiHMes2) with B(C6F5)3 rapidly produced HSiR3 in quantitative yield along with unidentified hafnium-containing species. However, reactions of Cp2Hf(SiR3)Me (SiR3 = Si(SiMe3)3 (8), SitBuPh2 (9), SiPh3 (10)) with B(C6F5)3 quantitatively produced the corresponding cationic hafnium silyl complexes 12-14. The complex Cp2Hf(SitBuPh2)(mu-Me)B(C6F5)3 (13) was isolated by crystallization from toluene at -30 degrees C and fully characterized, and its spectroscopic properties and crystal structure are compared to those of its neutral precursor 9. The sigma-bond metathesis reaction of 13 with Mes2SiH2 yielded HSitBuPh2 and the reactive species Cp2Hf(eta(2)-SiHMes2)(mu-Me)B(C6F5)3 (16, benzene-d6), which was also generated by reaction of Cp2Hf(SiMes2H)Me (11) with B(C6F5)3. Spectroscopic data provide evidence for an unusual alpha-agostic Si-H interaction in 16. At room temperature, 16 reacts with benzene to form Cp2Hf(Ph)(mu-Me)B(C6F5)3 (17), and with toluene to give isomers of Cp2Hf(C6H4Me)(mu-Me)B(C6F5)3 (18-20) and Cp2Hf(CH2Ph)(mu-Me)B(C6F5)3 (21). The reaction with benzene is first order in both 16 and benzene. Kinetic data including activation parameters (deltaH = 19(1) kcal/mol; deltaS = -17(3) eu), a large primary isotope effect (kH/kD = 6.9(7)), and the experimentally determined rate law are consistent with a mechanism involving a concerted transition state for C-H bond activation.     

Cationic Rh complexes with novel spiro tetraarylpentaborate anions prepared from arylboronic acids and aryloxorhodium complexes

Ar-B(OH)2 (1a: Ar = C6H4OMe-4, 1b: Ar = C6H3Me2-2,6) react immediately with Rh(OC6H4Me-4)(PMe3)3 (2) in 5 : 1 molar ratio at room temperature to generate [Rh(PMe3)4]+[B5O6Ar4]- (3a: Ar = C6H4OMe-4, 3b: Ar = C6H3Me2-2,6). p-Cresol (92%/Rh), anisole (80%/Rh) and H2O (364%/Rh) are formed from 1a and 2. The reaction of 1a with 2 for 24 h produces [Rh(PMe3)4]+[B5O6(OH)4]- (4) as a yellow solid. This is attributed to hydrolytic dearylation of once formed 3a because the direct reaction of 3a with excess H2O forms 4. An equimolar reaction of 2 with phenylboroxine (PhBO)3 causes transfer of the 4-methylphenoxo ligand from rhodium to boron to produce [Rh(PMe3)4]+[B3O3Ph3(OC6H4Me-4)]- (5). Arylboronic acids 1a and 1b react with Rh(OC6H4Me-4)(PR3)3 (6: R = Et, 8: R = Ph) and with Rh(OC6H4Me-4)(cod)(PR3) (11: R = iPr, 12: R = Ph) to form [Rh(PR3)4]+[B5O6Ar4]- (7a: R = Et, Ar = C6H4OMe-4, 7b: R = Et, Ar = C6H3Me2-2,6, 9a: R = Ph, Ar = C6H3Me2-2,6) and [Rh(cod)(PR3)(L)]+[B5O6Ar4]- (13b: R = iPr, L = acetone, Ar = C6H3Me2-2,6, 14a: R = Ph, L = PPh3, Ar = C6H4OMe-4, 14b: R = Ph, L = PPh3, Ar = C6H3Me2-2,6), respectively. Hydrolysis of 14a yields [Rh(cod)(PPh3)2]+[B5O6(OH)4]- (15) quantitatively.     

Structures and reactivity of Zr(IV) chlorobenzene complexes

The synthesis, structures, and unusual reactivity of (C5R5)2ZrR'(ClPh)+ chlorobenzene complexes are described. The reaction of (C5R5)2ZrR'2 with [Ph3C][B(C6F5)4] in C6D5Cl affords [(C5R5)2ZrR'(ClC6D5)][B(C6F5)4] chlorobenzene complexes (1-d5, R' = CH2Ph and (C5R5)2 = (C5H5)2; 2a-d-d5, R' = Me and (C5R5)2 = rac-(1,2-ethylene(bis)indenyl) (2a), (C5H5)2 (2b), (C5H4Me)2 (2c), (C5Me5)2 (2d, C5Me5 = Cp*)). Complexes 1 and 2b,c are thermally robust but are converted to [{(C5R5)2Zr(mu-Cl)}2][B(C6F5)4]2 (4b,c) by a photochemical process in ClPh solution. In contrast, 2d undergoes facile thermal ortho-C-H activation to yield [Cp*2Zr(eta2-C,Cl-2-Cl-C6H4)][B(C6F5)4] (5), which slowly rearranges to [(eta4,eta1-C5Me5C6H4)Cp*ZrCl][B(C6F5)4] (6) via beta-Cl elimination and benzyne insertion into a Zr-CCp* bond. The higher thermal reactivity of 2d versus that of 1 and 2b,c is attributed to steric crowding associated with the Cp* ligands of 2d, which forces a ClPh ortho-hydrogen close to the Zr-Me group.     

Mixed Bis(μ-silylene) and (μ-Silylene)/(μ-Germylene) Complexes Involving the Rh/Ir Metal Combination: Nature of the Si···Si Interactions in the Bis(μ-silylene) Species

A series of mixed bis(μ-silylene) complexes of rhodium and iridium [RhIr(CO)(2)(μ-SiHR)(μ-SiR(1)R(2))(dppm)(2)] (R = R(1) = R(2) = Ph (4); R = R(1) = Ph, R(2) = Cl (5); R = R(1) = Ph, R(2) = Me (6); R = 3,5-C(6)H(3)F(2), R(1) = Ph, R(2) = Me (7); R = 3,5-C(6)H(3)F(2), R(1) = 2,4,6-C(6)H(2)Me(3), R(2) = H (8)) have been synthesized by the reaction of the silylene-bridged dihydride complexes, [RhIr(H)(2)(CO)(2)(μ-SiHR)(dppm)(2)] (1, R = Ph; 2, R = C(6)H(3)F(2)), with a number of secondary or primary silanes (Ph(2)SiH(2), PhClSiH(2), PhMeSiH(2), C(6)H(2)Me(3)SiH(3)). The influence of substituents and π-stacking interactions on the Si···Si distance (determined by X-ray crystallography) in this series and the implications regarding the nature of the Si···Si interactions are discussed. A series of novel (μ-silylene)/(μ-germylene) complexes, [RhIr(CO)(2)(μ-SiHPh)(μ-GePh(2))(dppm)(2)] (9) and [RhIr(CO)(2)(μ-SiR(1)R(2))(μ-GeHPh)(dppm)(2)] (R(1) = Ph, R(2) = H (11); R(1) = R(2) = Ph (12); R(1) = Ph, R(2) = Me (13)), have also been synthesized by reaction of the silylene-bridged dihydride complex, [RhIr(H)(2)(CO)(2)(μ-SiHPh)(dppm)(2)] (1), with 1 equiv of diphenylgermane and by reaction of the germylene-bridged dihydride complex, [RhIr(H)(2)(CO)(2)(μ-GeHPh)(dppm)(2)] (3), with 1 equiv of the respective silanes. These complexes have been characterized by multinuclear NMR spectroscopy and X-ray crystallography.     

Synthesis and reactivity of tris(imido)rhenium complexes containing rhenium-main group element bonds. silicon-carbon bond activations of PhSiH(3) by silyl complexes

The synthesis and reactivity of a series of complexes of the (DippN=)(3)Re (Dipp = 2,6-(i)Pr(2)C(6)H(3)) fragment are reported. The anionic, Re(V) complex (THF)(2)Li(micro,micro-NDipp)(2)Re(=NDipp) (1), prepared by the reaction of (DippN=)(3)ReCl with (THF)(3)LiSi(SiMe(3))(3) or (t)BuLi (2 equiv) in the presence of THF (4 equiv), served as an important starting material for the synthesis of rhenium-element-bonded complexes. For example, treatment of 1 with ClSiR(3) gave the corresponding silyl complexes (DippN=)(3)ReSiR(3) (SiR(3) = SiMe(3) (2a), SiHPh(2) (2b), SiH(2)Ph (2c)). Complexes 2a-c are thought to exist in equilibrium between the Re(VII) (DippN=)(3)ReSiR(3) and Re(V) (DippN=)(2)ReN(SiR(3))Dipp isomers. Complexes 2a,b reacted with PhSiH(3) to give reaction mixtures that included 2c, Ph(2)SiH(2), SiH(4), and C(6)H(6). The silane and organic products arise from Si-C bond formation and cleavage. Treatment of 2a with CO gave (DippN=)(2)Re[N(SiMe(3))Dipp](CO) (3), which appears to result from trapping of the reactive Re(V) isomer of 2a by CO. Complex 1 reacted with the main group halides MeI, Ph(3)GeCl, Me(3)SnCl, Ph(2)PCl, and PhSeCl to give the corresponding rhenium complexes (DippN=)(3)ReER(n) (ER(n)() = Me (4), GePh(3) (5), SnMe(3) (6), PPh(2) (7), SePh (8)) in high yields. X-ray diffraction data for 5 indicate that the germyl ligand is bonded to rhenium, but positional disorder of the phenyl and Dipp groups prevented refinement of accurate metric parameters.     

Half-sandwich bis(tetramethylaluminate) complexes of the rare-earth metals: synthesis, structural chemistry, and performance in isoprene polymerization

The protonolysis reaction of [Ln(AlMe(4))(3)] with various substituted cyclopentadienyl derivatives HCp(R) gives access to a series of half-sandwich complexes [Ln(AlMe(4))(2)(Cp(R))]. Whereas bis(tetramethylaluminate) complexes with [1,3-(Me(3)Si)(2)C(5)H(3)] and [C(5)Me(4)SiMe(3)] ancillary ligands form easily at ambient temperature for the entire Ln(III) cation size range (Ln=Lu, Y, Sm, Nd, La), exchange with the less reactive [1,2,4-(Me(3)C)(3)C(5)H(3)] was only obtained at elevated temperatures and for the larger metal centers Sm, Nd, and La. X-ray structure analyses of seven representative complexes of the type [Ln(AlMe(4))(2)(Cp(R))] reveal a similar distinct [AlMe(4)] coordination (one eta(2), one bent eta(2)). Treatment with Me(2)AlCl leads to [AlMe(4)] --> [Cl] exchange and, depending on the Al/Ln ratio and the Cp(R) ligand, varying amounts of partially and fully exchanged products [{Ln(AlMe(4))(mu-Cl)(Cp(R))}(2)] and [{Ln(mu-Cl)(2)(Cp(R))}(n)], respectively, have been identified. Complexes [{Y(AlMe(4))(mu-Cl)(C(5)Me(4)SiMe(3))}(2)] and [{Nd(AlMe(4))(mu-Cl){1,2,4-(Me(3)C)(3)C(5)H(2)}}(2)] have been characterized by X-ray structure analysis. All of the chlorinated half-sandwich complexes are inactive in isoprene polymerization. However, activation of the complexes [Ln(AlMe(4))(2)(Cp(R))] with boron-containing cocatalysts, such as [Ph(3)C][B(C(6)F(5))(4)], [PhNMe(2)H][B(C(6)F(5))(4)], or B(C(6)F(5))(3), produces initiators for the fabrication of trans-1,4-polyisoprene. The choice of rare-earth metal cation size, Cp(R) ancillary ligand, and type of boron cocatalyst crucially affects the polymerization performance, including activity, catalyst efficiency, living character, and polymer stereoregularity. The highest stereoselectivities were observed for the precatalyst/cocatalyst systems [La(AlMe(4))(2)(C(5)Me(4)SiMe(3))]/B(C(6)F(5))(3) (trans-1,4 content: 95.6 %, M(w)/M(n)=1.26) and [La(AlMe(4))(2)(C(5)Me(5))]/B(C(6)F(5))(3) (trans-1,4 content: 99.5 %, M(w)/M(n)=1.18).     

Novel eta 3 -1-silaallyl tungsten complexes via Si-H bond activation of hydrovinylsilanes: structure and reactivity toward methanol

Reactions of cis-Cp*(CO)2W(MeCN)Me (1) with HSiMe2(CH=CR2) (R = H, Me) afford the novel eta3-1-silaallyl complexes Cp*(CO)2W(eta3-Me2SiCHCR2) [R = H (2), Me (3)] accompanied by liberation of MeCN and CH4 via thermal Si-H bond activation. eta3-Coordination and exo conformation of the 1-silaallyl ligand in 3 are shown by X-ray crystal analysis, which reveals the partial double bond character of the Si-C bond (1.800(4) A) in the silaallyl moiety. Complexes 2 and 3 show extremely high reactivity toward MeOH to give the hydrido-(methoxysilyl)alkene complex trans-Cp*(CO)2WH(eta2-MeOMe2SiCH=CH2) (4) and the four-membered metallacycle Cp*(CO)2WCH(CHMe2)SiMe2OMe (6), respectively.     

Synthesis, characterization, and activity in ethylene polymerization of silica supported cationic cyclopentadienyl zirconium complexes

Cp*ZrMe3 reacts with silica pretreated at 800 degrees C, SiO(2-(800)) through two pathways: (a) protolysis of a Zr-Me group by surface silanols and (b) transfer of a methyl group to the surface by opening of strained siloxane bridges, in a relative proportion of ca. 9/1, respectively, affording a well-defined surface species [([triple bond]SiO)ZrCp*(Me)2], 3, but with two different local environments 3a, [([triple bond]SiO)ZrCp*(Me)2][[triple bond]Si-O-Si[triple bond]], and the other with 3b, [structure: see text]. The reaction of the species 3 with B(C6F5)3 is controlled by this local environment and gives three surface species [([triple bond]SiO)ZrCp*(Me)](+)[MeB(C6F5)3]- [[triple bond]Si-O-Si[triple bond]], 4a (20%), [([triple bond]SiO)ZrCp*(Me)](+)[(Me)B(C6F5)3]- [[triple bond]Si-Me], 4b (10%), and [([triple bond]SiO)2ZrCp*](+)[(Me)B(C6F5)(3)](-)[[triple bond]Si-O-Si[triple bond]], 5 (70%). On the contrary, the reaction of Cp*Zr(Me)3, Cp2Zr(Me)2 with [[triple bond]SiO-B(C6F5)3](-)[HNEt2Ph]+, 6, leads to a unique species [([triple bond]SiO)B(C6F5)3](-)[Cp*Zr(Me)2.NEt2Ph]+, 7, and [([triple bond]SiO)ZrCp2](+)[(Me)B(C6F5)3]-, 9 respectively. The complexes 4 and 7 are active catalysts in ethylene polymerization at room temperature, 93 and 67 kg PE mol Zr1- atm(-1) bar(-1), respectively, indicating that covalently bounded Zr catalyst 4 is slightly more active than the "floating" cationic catalyst 7.     

Trapping reactions of an intermediate containing a tungsten-phosphorus triple bond with alkynes

The thermolysis of the phosphinidene complex [Cp*P[W(CO)5]2] (1) in toluene in the presence of tBuC(triple bond)CMe leads to the four-membered ring complexes [[[eta2-C(Me)C(tBu)]Cp*(CO)W(mu3-P)[W(CO)3]][eta4:eta1:eta1-P[W(CO)5]WCp*(CO)C(Me)C(tBu)]] (4) as the major product and [[W[Cp*(CO)2]W(CO)2WCp*(CO)[eta1:eta1-C(Me)C(tBu)]](mu,eta3:eta2:eta1-P2[W(CO)5]] (5). The reaction of 1 with PhC(triple bond)CPh leads to [[W(Co)2[eta2-C(Ph)C(Ph)]][(eta4:eta1-P(W(CO)5]W[Cp*(CO)2)C(Ph)C(Ph)]] (6). The products 4 and 6 can be regarded as the formal cycloaddition products of the phosphido complex intermediate [Cp*(CO)2W(triple bond)P --> W(CO)5] (B), formed by Cp* migration within the phosphinidene complex 1. Furthermore, the reaction of 1 with PhC(triple bond)CPh gives the minor product [[[eta2:eta1-C(Ph)C(Ph)]2[W(CO)4]2][mu,eta1:eta1-P[C(Me)[C(Me)]3C(Me)][C(Ph)](C(Ph)]] (7) as a result of a 1,3-dipolaric cycloaddition of the alkyne into a phosphaallylic subunit of the Cp*P moiety of 1. Compounds 4-7 have been characterized by means of their spectroscopic data as well as by single-crystal X-ray structure analysis.     

Group 6 imido complexes supported by diamido-donor ligands

Reactions of the lithiated diamido-pyridine or diamido-amine ligands Li(2)N(2)N(py) or Li(2)N(2)N(am) with [W(NAr)Cl(4)(THF)] (Ar = Ph or 2,6-C(6)H(3)Me(2); THF = tetrahydrofuran) afforded the corresponding imido-dichloride complexes [W(NAr)(N(2)N(py))Cl(2)] (R = Ph, 1, or 2,6-C(6)H(3)Me(2), 2) or [W(NAr)(N(2)N(am))Cl(2)] (R = Ph, 3, or 2,6-C(6)H(3)Me(2), 4), respectively, where N(2)N(py) = MeC(2-C(5)H(4)N)(CH(2)NSiMe(3))(2) and N(2)N(am) = Me(3)SiN(CH(2)CH(2)NSiMe(3))(2). Subsequent reactions of 1 with MeMgBr or PhMgCl afforded the dimethyl or diphenyl complexes [W(NPh)(N(2)N(py))R(2)] (R = Me, 5, or Ph, 6), respectively, which have both been characterized by single crystal X-ray diffraction. Reactions of Li(2)N(2)N(py) or Li(2)N(2)N(am) with [Mo(NR)(2)Cl(2)(DME)] (R = (t)Bu or Ph; DME = 1,2-dimethoxyethane) afforded the corresponding bis(imido) complexes [Mo(NR)(2)(N(2)N(py))] (R = (t)Bu, 7, or Ph, 8) and [Mo(N(t)Bu)(2)(N(2)N(am))] (9).     

Titanium "constrained geometry" complexes with pendant arene groups

The synthesis of the proligands C(5)Me(4)HSiMe(2)N(H)R) (R = CMe(2)Ph 1, 2-C(6)H(4)Ph 2) was accomplished via a straightforward salt metathesis reaction of the appropriate lithium amide and ClSiMe(2)(C(5)Me(5)H). Generation of the dilithio salt and reaction with TiCl(3)·(THF)(3) followed by oxidation gave C(5)Me(4)SiMe(2)N(C(6)H(4)Ph)TiCl(2) (3) in low yield. In contrast, deprotonation of 1 and 2 and reaction with (Me(2)N)(2)TiCl(2) afforded C(5)Me(4)(SiMe(2)NR)Ti(NMe(2))(2) (R = CMe(2)Ph 4, 2-C(6)H(4)Ph 5), respectively, in good yields Treatment with MeI gave the analogs C(5)Me(4)(SiMe(2)NR)TiI(2) (R = CMe(2)Ph 6, 2-C(6)H(4)Ph 7). Reduction of 7 with potassium graphite afforded C(5)Me(4)(SiMe(2)NC(6)H(4)Ph)Ti 8. Treatment of 6 and 7 with MeMgBr afforded C(5)Me(4)(SiMe(2)NR)TiMe(2) (R = CMe(2)Ph 9, 2-C(6)H(4)Ph 10). Complexes 9 and 10 in combination with the activator [Ph(3)C][B(C(6)F(5))(4)] catalyzed the polymerization of styrene and ethylene. Copolymerization was also investigated. While the catalyst derived from 10 showed poor activity, compound 9 showed markedly higher activity than 10 and (C(5)Me(4))SiMe(2)(NtBu)]TiMe(2).