Constrained geometry organoactinides as versatile catalysts for the intramolecular hydroamination/cyclization of primary and secondary amines having diverse tethered C-C unsaturation

A series of "constrained geometry" organoactinide complexes, (CGC)An(NMe)2 (CGC = Me2Si(eta5-Me4C5)(tBuN); An = Th, 1; U, 2), has been prepared via efficient in situ, two-step protodeamination routes in good yields and high purity. Both 1 and 2 are quantitatively converted to the neutrally charged, solvent-free dichlorides (1-Cl2, 2-Cl2) and slightly more soluble diiodides (1-I2, 2-I2) with excess Me3Si-X (X = Cl, I) in non-coordinating solvents. The new complexes were characterized by NMR spectroscopy, elemental analysis, and (for 1 and 2) single-crystal X-ray diffraction, revealing substantially increased metal coordinative unsaturation vs the corresponding Me2SiCp' '2AnR2 (Cp' ' = eta5-Me4C5; An = Th, R = CH2(SiMe3), 3; An = U, R = CH2Ph, 4) and Cp'2AnR2 (Cp' = eta5-Me5C5 ; An = Th, R = CH2(SiMe3), 5; An = U, R = CH2(SiMe3), 6) complexes. Complexes 1-6 exhibit broad applicability for the intramolecular hydroamination of diverse C-C unsaturations, including terminal and internal aminoalkenes (primary and secondary amines), aminoalkynes (primary and secondary amines), aminoallenes, and aminodienes. Large turnover frequencies (Nt up to 3000 h-1) and high regioselectivities (>/=95%) are observed throughout, along with moderate to high diastereoselectivities (up to 90% trans ring closures). With several noteworthy exceptions, reactivity trends track relative 5f ionic radii and ancillary ligand coordinative unsaturation. Reactivity patterns and activation parameters are consistent with a reaction pathway proceeding via turnover-limiting C=C/CC insertion into the An-N sigma-bond.     

Organolathanide-catalyzed regioselective intermolecular hydroamination of alkenes, alkynes, vinylarenes, di- and trivinylarenes, and methylenecyclopropanes. Scope and mechanistic comparison to intramolecular cyclohydroaminations

Organolanthanide complexes of the type Cp'(2)LnCH(SiMe(3))(2) (Cp' = eta(5)-Me(5)C(5); Ln = La, Nd, Sm, Lu) and Me(2)SiCp' '(2)LnCH(SiMe(3))(2) (Cp' ' = eta(5)-Me(4)C(5); Ln = Nd, Sm, Lu) serve as efficient precatalysts for the regioselective intermolecular hydroamination of alkynes R'Ctbd1;CMe (R' = SiMe(3), C(6)H(5), Me), alkenes RCH=CH(2) (R = SiMe(3), CH(3)CH(2)CH(2)), butadiene, vinylarenes ArCH=CH(2) (Ar = phenyl, 4-methylbenzene, naphthyl, 4-fluorobenzene, 4-(trifluoromethyl)benzene, 4-methoxybenzene, 4-(dimethylamino)benzene, 4-(methylthio)benzene), di- and trivinylarenes, and methylenecyclopropanes with primary amines R' 'NH(2) (R' ' = n-propyl, n-butyl, isobutyl, phenyl, 4-methylphenyl, 4-(dimethylamino)phenyl) to yield the corresponding amines and imines. For R = SiMe(3), R = CH(2)=CH lanthanide-mediated intermolecular hydroamination regioselectively generates the anti-Markovnikov addition products (Me(3)SiCH(2)CH(2)NHR' ', (E)-CH(3)CH=CHCH(2)NHR' '). However, for R = CH(3)CH(2)CH(2), the Markovnikov addition product is observed (CH(3)CH(2)CH(2)CHNHR' 'CH(3)). For internal alkynes, it appears that these regioselective transformations occur under significant stereoelectronic control, and for R' = SiMe(3), rearrangement of the product enamines occurs via tautomerization to imines, followed by a 1,3-trimethylsilyl group shift to stable N-SiMe(3)-bonded CH(2)=CMeN(SiMe(3))R' ' structures. For vinylarenes, intermolecular hydroamination with n-propylamine affords the anti-Markovnikov addition product beta-phenylethylamine. In addition, hydroamination of divinylarenes provides a concise synthesis of tetrahydroisoquinoline structures via coupled intermolecular hydroamination/subsequent intramolecular cyclohydroamination sequences. Intermolecular hydroamination of methylenecyclopropane proceeds via highly regioselective exo-methylene C=C insertion into Ln-N bonds, followed by regioselective cyclopropane ring opening to afford the corresponding imine. For the Me(2)SiCp' '(2)Nd-catalyzed reaction of Me(3)SiCtbd1;CMe and H(2)NCH(2)CH(2)CH(2)CH(3), DeltaH() = 17.2 (1.1) kcal mol(-)(1) and DeltaS() = -25.9 (9.7) eu, while the reaction kinetics are zero-order in [amine] and first-order in both [catalyst] and [alkyne]. For the same substrate pair, catalytic turnover frequencies under identical conditions decrease in the order Me(2)SiCp' '(2)NdCH(SiMe(3))(2) > Me(2)SiCp' '(2)SmCH(SiMe(3))(2) > Me(2)SiCp' '(2)LuCH(SiMe(3))(2) > Cp'(2)SmCH(SiMe(3))(2), in accord with documented steric requirements for the insertion of olefinic functionalities into lanthanide-alkyl and -heteroatom sigma-bonds. Kinetic and mechanistic evidence argues that the turnover-limiting step is intermolecular C=C/Ctbd1;C bond insertion into the Ln-N bond followed by rapid protonolysis of the resulting Ln-C bond.     

Synthesis, structural characterization, reactivity, and thermal stability of [eta(5):sigma-Me2C(C5H4)(C2B10H10)]Ti(R)(NMe2)

Reaction of [eta:(5)sigma-Me2C(C5H4)(C2B10H10)]TiCl(NMe2) (1) with 1 equiv of PhCH2K, MeMgBr, or Me3SiCH2Li gave corresponding organotitanium alkyl complexes [eta:(5)sigma-Me2C(C5H4)(C2B10H10)]Ti(R)(NMe2) (R = CH2Ph (2), CH2SiMe3 (4), or Me (5)) in good yields. Treatment of 1 with 1 equiv of n-BuLi afforded the decomposition product {[eta:(5)sigma-Me2C(C5H4)(C2B10H10)]Ti}2(mu-NMe)(mu:sigma-CH2NMe) (3). Complex 5 slowly decomposed to generate a mixed-valence dinuclear species {[eta:(5)sigma-Me2C(C5H4)(C2B10H10)]Ti}2(mu-NMe2)(mu:sigma-CH2NMe) (6). Complex 1 reacted with 1 equiv of PhNCO or 2,6-Me2C6H3NC to afford the corresponding monoinsertion product [eta:(5)sigma-Me2C(C5H4)(C2B10H10)]Ti(Cl)[eta(2)-OC(NMe2)NPh] (7) or [eta:(5)sigma-Me2C(C5H4)(C2B10H10)]Ti(Cl)[eta(2)-C(NMe2)=N(2,6-Me2C6H3)] (8). Reaction of 4 or 5 with 1 equiv of R'NC gave the titanium eta(2)-iminoacyl complexes [eta:(5)sigma-Me2C(C5H4)(C2B10H10)]Ti(NMe2)[eta(2)-C(R)=N(R')] (R = CH2SiMe3, R' = 2,6-Me2C6H3 (9) or tBu (10); R = Me, R' = 2,6-Me2C6H3 (11) or tBu (12)). The results indicated that the unsaturated molecules inserted into the Ti-N bond only in the absence of the Ti-C(alkyl) bond and that the Ti-C(cage) bond remained intact. All complexes were fully characterized by various spectroscopic techniques and elemental analyses. Molecular structures of 2, 3, 6-8, and 10-12 were further confirmed by single-crystal X-ray analyses.     

Highly stereoselective intramolecular hydroamination/cyclization of conjugated aminodienes catalyzed by organolanthanides

Efficient intramolecular hydroamination/cyclization of primary and secondary conjugated aminodienes can be effected by using organolanthanide precatalysts of the type Cp'2LnCH(TMS)2 (Cp' = eta5-Me5C5; Ln = La, Sm, Y; TMS = SiMe3) and CGCSmN(TMS)2 (CGC = Me2Si(eta5-Me4C5)(tBuN)). The transformation proceeds cleanly (>/= 90% conversion) at 25-60 degrees C with good rates and high regioselectivities, and with electronic effects leading to significant rate enhancements. Some features of the reaction parallel monosubstituted aminoalkene hydroamination/cyclization, including rate law (zero order in [aminodiene]), and rate enhancements observed with larger lanthanide ionic radii and/or more open catalyst ligation structures. Good to excellent diastereoselectivity is obtained in the synthesis of 2,5-trans-disubstituted pyrrolidines (80% de) and 2,6-cis-disubstituted piperidines (99% de) with using the corresponding alpha-methyl aminodiene precursors. Formation of 2-(prop-1-enyl)piperidine with the chiral C1-symmetric precatalyst (S)-Me2Si(OHF)(CpR*)SmN(TMS)2 (OHF = eta5-octahydrofluorenyl; Cp = eta5-C5H3; R* = (-)-menthyl) proceeds with up to 69% ee.     

Alkyl-eta2-alkene niobocene and tantalocene complexes with the allyldimethylsilyl-eta5-cyclopentadienyl ligand: synthesis, NMR studies and DFT calculations

Group 5 metal complexes [M(eta5-C5H5)[eta5-C5H4SiMe2(CH2-eta]2-CH=CH2)]X] (M = Nb, X = Me, CH2Ph, CH2SiMe3; M = Ta, X = Me, CH2Ph) and [Ta(eta5-C5Me5)[eta5-C5H4SiMe2(CH2-eta2-CH=CH2)]X] (X = Cl, Me, CH2Ph, CH2SiMe3) containing a chelating alkene ligand tethered to a cyclopentadienyl ring have been synthesized in high yields by reduction with Na/Hg (X = Cl) and alkylation with reductive elimination (X = alkyl) of the corresponding metal(iv) dichlorides [M(eta5-Cp)[eta5-C5H4SiMe2(CH2CH=CH2)]Cl2] (Cp = C5H5, M = Nb, Ta, Cp = C5Me5, M = Ta). These chloro- and alkyl-alkene coordinated complexes react with CO and isocyanides [CNtBu, CN(2,6-Me2C6H3)] to give the ligand-substituted metal(III) compounds [M(eta5-Cp)[eta5-C5H4SiMe2(CH2CH=CH2)]XL] (X = Cl, Me, CH2Ph, CH2SiMe3). Reaction of the chloro-alkene tantalum complex with LiNHtBu results in formation of the imido hydride derivative [Ta(eta5-C5Me5)[eta5-C5H4SiMe2(CH2CH=CH2)]H(NtBu)]. NMR studies for all of the new compounds and DFT calculations for the alkene-coordinated metal complexes are compared with those known for related group 4 metal cations.     

Intramolecular hydroamination/cyclization of conjugated aminodienes catalyzed by organolanthanide complexes. Scope, diastereo- and enantioselectivity, and reaction mechanism

Organolanthanide complexes of the general type Cp'(2)LnCH(TMS)(2) (Cp' = eta(5)-Me(5)C(5); Ln = La, Sm, Y; TMS = SiMe(3)) and CGCSmN(TMS)(2) (CGC = Me(2)Si(eta(5)-Me(4)C(5))((t)()BuN)) serve as effective precatalysts for the rapid, regioselective, and highly diastereoselective intramolecular hydroamination/cyclization of primary and secondary amines tethered to conjugated dienes. The rates of aminodiene cyclizations are significantly more rapid than those of the corresponding aminoalkenes. This dienyl group rate enhancement as well as substituent group (R) effects on turnover frequencies is consistent with proposed transition state electronic demands. Kinetic and mechanistic data parallel monosubstituted aminoalkene hydroamination/cyclization, with turnover-limiting C=C insertion into the Ln-N bond to presumably form an Ln-eta(3) allyl intermediate, followed by rapid protonolysis of the resulting Ln-C linkage. The rate law is first-order in [catalyst] and zero-order in [aminodiene]. However, depending on the particular substrate and catalyst combination, deviations from zero-order kinetic behavior reflect competitive product inhibition or self-inhibition by substrate. Lanthanide ionic radius effects and ancillary ligation effects on turnover frequencies suggest a sterically more demanding Ln-N insertion step than in aminoalkene cyclohydroamination, while a substantially more negative DeltaS( double dagger ) implies a more highly organized transition state. Good to excellent diastereoselectivity is obtained in the synthesis of 2,5-trans-disubstituted pyrrolidines (80% de) and 2,6-cis-disubstituted piperidines (99% de). Formation of 2-(prop-1-enyl)piperidine using the chiral C(1)-symmetric precatalyst (S)-Me(2)Si(OHF)(CpR)SmN(TMS)(2) (OHF = eta(5)-octahydrofluorenyl; Cp = eta(5)-C(5)H(3); R = (-)-menthyl) proceeds with up to 71% ee. The highly stereoselective feature of aminodiene cyclization is demonstrated by concise syntheses of naturally occurring alkaloids, (+/-)-pinidine and (+)-coniine from simple diene precursors.     

Organolanthanide-catalyzed intramolecular hydroamination/cyclization/bicyclization of sterically encumbered substrates. Scope, selectivity, and catalyst thermal stability for amine-tethered unactivated 1,2-disubstituted alkenes

This paper reports the organolanthanide-catalyzed intramolecular hydroamination/cyclization of amine-tethered unactivated 1,2-disubstituted alkenes to afford the corresponding mono- and disubstituted pyrrolidines and piperidines using coordinatively unsaturated complexes of the type (eta(5)-Me(5)C(5))(2)LnCH(TMS)(2) (Ln = La, Sm), [Me(2)Si(eta(5)-Me(4)C(5))(2)]SmCH(TMS)(2), and [Me(2)Si(eta(5)-Me(4)C(5))((t)BuN)]LnE(TMS)(2) (Ln = Sm, Y, Yb, Lu; E = N, CH) as precatalysts. [Me(2)Si(eta(5)-Me(4)C(5))((t)BuN)]LnE(TMS)(2) mediates intramolecular hydroamination/cyclization of sterically demanding amino-olefins to afford disubstituted pyrrolidines in high diastereoselectivity (trans/cis = 16/1) and good to excellent yield. In addition, chiral C(1)-symmetric organolanthanide catalysts of the type [Me(2)Si(OHF)(CpR*)]LnN(TMS)(2) (OHF = eta(5)-octahydrofluorenyl; Cp = eta(5)-C(5)H(3); R* = (-)-menthyl; Ln = Sm, Y), and [Me(2)Si(eta(5)-Me(4)C(5))(CpR*)]SmN(TMS)(2) (Cp = eta(5)-H(3)C(5); R* = (-)-menthyl) mediate asymmetric intramolecular hydroamination/cyclization of amines bearing internal olefins and afford chiral 2-substituted piperidine and pyrrolidine in enantioselectivities as high as 84:16 er at 60 degrees C. The substrate of the structure NH(2)CH(2)CMe(2)CH(2)CH=CH(CH(2))(2)CH=CH(2) is regiospecifically bicyclized by [Me(2)Si(eta(5)-Me(4)C(5))((t)BuN)]LnE(TMS)(2) to the corresponding indolizidine skeleton in good yield and high diastereoselectivity. Thermolysis of (eta(5)-Me(5)C(5))(2)LaCH(TMS)(2) in cyclohexane-d(12) at 120 degrees C rapidly releases CH(2)(SiMe(3))(2) and leads to possible formation of fulvene (eta(6)-Me(4)C(5)CH(2)-) species. The thermolysis product readily reverts to active catalysts upon protonolysis by substrate and exhibits the same catalytic activity as the (eta(5),eta(1)-Me(5)C(5))(2)LaCH(TMS)(2) precatalyst at 120 degrees C in the cyclization of cis-2,2-dimethylhept-5-enylamine. Catalytically-active lanthanide-amido complexes (eta(5)-Me(5)C(5))(2)La(NHR)(NH(2)R)(n) and [Me(2)Si(eta(5)-Me(4)C(5))((t)BuN)]Sm(NHR)(NH(2)R)(n) are shown to be thermally robust species.     

Synthesis and structures of the C5Me4SiMe3-supported polyhydride complexes over the full size range of the rare earth series

The acid-base reaction of [Ln(CH(2)SiMe(3))(3)(thf)(2)] with Cp'H gave the corresponding half-sandwich rare earth dialkyl complexes [(Cp')Ln(CH(2)SiMe(3))(2)(thf)] (1-Ln: Ln=Sc, Y, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu; Cp'=C(5)Me(4)SiMe(3)) in 62-90% isolated yields. X-ray crystallographic studies revealed that all of these complexes adopt a similar overall structure, in spite of large difference in metal-ion size. In most cases, the hydrogenolysis of the dialkyl complexes in toluene gave the tetranuclear octahydride complexes [{(Cp')Ln(μ-H)(2)}(4)(thf)(x)] (2-Ln: Ln=Sc, x=0; Y, x=1; Er, x=1; Tm, x=1; Gd, x=1; Dy, x=1; Ho, x=1) as the only isolable product. However, in the case of Lu, a trinuclear pentahydride [(Cp')(2)Lu(3)(μ-H)(5)(μ-CH(2)SiMe(2)C(5)Me(4))(thf)(2)] (3), in which the C-H activation of a methyl group of the Me(3)Si unit on a Cp' ligand took place, was obtained as a major product (66% yield), in addition to the tetranuclear octahydride [{(Cp')Lu(μ-H)(2)}(4)(thf)] (2-Lu, 34%). The use of hexane instead of toluene as a solvent for the hydrogenolysis of 1-Lu led to formation of 2-Lu as a major product (85%), while a similar reaction in THF yielded 3 predominantly (90%). The tetranuclear octahydride complexes of early (larger) lanthanide metals [{Cp'Ln(μ-H)(2)}(4)(thf)(2)] (2, Ln=La, Ce, Pr, Nd, Sm) were obtained in 38-57% isolated yields by hydrogenolysis of the bis(aminobenzyl) species [Cp'Ln(CH(2)C(6)H(4)NMe(2)-o)(2)], which were generated in-situ by reaction of [Ln(CH(2)C(6)H(4)NMe(2)-o)(3)] with one equivalent of Cp'H. X-ray crystallographic studies showed that the fine structures of these hydride clusters are dependent on the size of the metal ions.     

o-Phenylene-bridged Cp/sulfonamido titanium complexes for ethylene/1-octene copolymerization

The Suzuki-coupling reaction of 2-(dihydroxyboryl)-3,4-dimethyl-2-cyclopenten-1-one and 2-(dihydroxyboryl)-3-methyl-2-cyclopenten-1-one with 2-bromoaniline derivatives affords cyclopentenone compounds from which cyclopentadiene compounds, 4,6-R'(2)-2-(2,5-Me2C5H3)C6H2NH2 and 4,6-R'(2)-2-(2,3,5-Me3C5H2)C6H2NH2 are prepared. After sulfonation of the -NH2 group with p-TsCl, metallation is carried out by successive addition of Ti(NMe2)4 and Me2SiCl2 affording o-phenylene-bridged Cp/sulfonamido titanium dichloride complexes, [4,6-R'(2)-2-(2,5-Me2C5H2)C6H2NSO2C6H4CH3)]TiCl2 (R'=H, ; R'=Me, ; R'=F, ) and [4,6-R'(2)-2-(2,3,5-Me3C5H)C6H2NSO2C6H4CH3)]TiCl2 (R'=H, ; R'=Me, ; R'=F, ). The molecular structures of and [2-(2,5-Me2C5H2)C6H4NSO2C6H4CH3)]Ti(NMe2)2 are determined by X-ray crystallography. The Cp(centroid)-Ti-N angle in is smaller (100.90 degrees) than that observed for the CGC (constrained-geometry catalyst), [Me2Si(eta5-Me4Cp)(NtBu)]TiCl2 (107.6 degrees) indicating a more "constrained feature" in than in the CGC. Complex shows the highest activity among the newly prepared complexes in ethylene/1-octene copolymerization but it is slightly inferior to the CGC in terms of activity, comonomer-incorporation ability, and molecular weight of the obtained polymers.     

Trialkyl imido niobium and tantalum compounds: synthesis, structural study and migratory insertion reactions

Trialkyl imido niobium and tantalum complexes [MR(3)(NtBu)] (M = Nb, R = Me 2, CH(2)CMe(3)3, CH(2)CMe(2)Ph 4, CH(2)SiMe(3)5; M = Ta, R = Me 6, CH(2)CMe(2)Ph 7, CH(2)SiMe(3)8) have been prepared by treatment of solutions containing [MCl(3)(NtBu)py(2)] (M = Nb 1a, Ta 1b) with three equivalents of magnesium reagent. By an unexpected hydrolysis reaction of the tris-trimethylsilylmethyl imido tantalum compound 8a, a μ-oxo derivative [(Me(3)SiCH(2)O)(Me(3)SiCH(2))(3)Ta(μ-O)Ta(CH(2)SiMe(3))(2)(NtBu)] (8a) was formed and its structure was studied by X-ray diffraction methods. Reactions of trialkyl imido compounds with two equivalents of isocyanide 2,6-Me(2)C(6)H(3)NC result in the migration of two alkyl groups, leading to the formation of a series of alkyl imido bisiminoacyl derivatives [MR(NtBu){C(R)NAr}(2)] (Ar = 2,6-Me(2)C(6)H(3); M = Nb, R = Me 9, CH(2)CMe(3)10, CH(2)CMe(2)Ph 11, CH(2)SiMe(3)12, CH(2)Ph 13; M = Ta, R = CH(2)CMe(3)14, CH(2)CMe(2)Ph 15, CH(2)SiMe(3)16). All compounds were studied by IR and NMR ((1)H, (13)C and (15)N) spectroscopy.     

Synthesis, structure, and reactivity of Group 4 metallacycles incorporating a Me2C-linked cyclopentadienyl-carboranyl ligand

Group 4 metallacycles [eta5:sigma-Me2C(C5H4)(C2B10H10)]Ti[eta2-N(Me)CH2CH2N(Me)] (1a), [eta5:sigma-Me2C(C5H4)(C2B10H10)]Zr[eta2-N(Me)CH2CH2N(Me)](HNMe2) (1b) and [eta5:sigma-Me2C(C5H4)(C2B10H10)]M[eta2-N(Me)CH2CH2CH2N(Me)] (M = Ti (2a), Zr (2b), Hf (2c)) were synthesized by reaction of [eta5:sigma-Me2C(C5H4)(C2B10H10)]M(NMe2)(2) (M = Ti, Zr, Hf) with MeNH(CH2)(n)NHMe (n = 2, 3). These metal complexes reacted with unsaturated molecules such as 2,6-Me2C6H3NC, PhNCO and PhCN to give exclusively M-N bond insertion products. The M-C(cage) bond remained intact. Such a preference of M-N over M-C(cage) insertion is suggested to most likely be governed by steric factors, and the mobility of the migratory groups plays no obvious role in the reactions. This work also shows that the insertion of unsaturated molecules into the metallacycles is a useful and effective method for the construction of very large ring systems.     

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.     

Synthetic, reactivity, and structural studies on half-sandwich (eta5-C5Me5)Be and related compounds: halide, alkyl, and iminoacyl derivatives

The half-sandwich compounds [(eta(5)-C(5)Me(5))BeX] (X=Cl, 1 a; Br, 1 b), readily prepared from the reaction of the halides BeX(2) and M[C(5)Me(5)] (M=Na or K), are useful synthons for other (eta(5)-C(5)Me(5))Be organometallic compounds, including the alkyl derivatives [(eta(5)-C(5)Me(5))BeR] (R=Me, 2 a; CMe(3), 2 b; CH(2)CMe(3), 2 c; CH(2)Ph, 2 d). The latter compounds can be obtained by metathetical exchange of the halides 1 with the corresponding lithium reagent and exhibit NMR signals and other properties in accord with the proposed formulation. Attempts to make [(eta(5)-C(5)Me(5))BeH] have proved fruitless, probably due to instability of the hydride toward disproportionation into [Be(C(5)Me(5))(2)] and BeH(2). The half-sandwich iminoacyl [(eta(5)-C(5)Me(5))Be(C(NXyl)Cp')] and [(eta(5)-C(5)Me(4)H)Be(C(NXyl)Cp')]3, 6 where Xyl=C(6)H(3)-2,6-Me(2) and Cp'=C(5)Me(5) or C(5)Me(4)H, are formed when the beryllocenes [Be(C(5)Me(5))(2)], [Be(C(5)Me(4)H)(2)], and [Be(C(5)Me(5))(C(5)Me(4)H)] are allowed to react with CNXyl. Isolation of three different iminoacyl isomers from the reaction of the mixed-ring beryllocene [(eta(5)-C(5)Me(5))Be(eta(1)-C(5)Me(4)H)] and CNXyl, namely compounds 5 a, 5 b, and 6, provides compelling evidence for the existence in solution of different beryllocene isomers, generated in the course of two very facile processes that explain the solution dynamics of these metallocenes, that is the 1,5-sigmatropic shift of the Be(eta(5)-Cp') unit around the periphery of the eta(1)-Cp' ring, and the molecular inversion rearrangement that exchanges the roles of the two rings.     

Ln4(CH2)4 cubane-type rare-earth methylidene complexes consisting of "(C5Me4SiMe3)LnCH2" units (Ln = Tm, Lu)

Tetranuclear cubane-type rare-earth methylidene complexes consisting of four "Cp'LnCH(2)" units, [Cp'Ln(μ(3)-CH(2))](4) (4-Ln; Ln = Tm, Lu; Cp' = C(5)Me(4)SiMe(3)), have been obtained for the first time through CH(4) elimination from the well-defined polymethyl complexes [Cp'Ln(μ(2)-CH(3))(2)](3) (2-Ln) or mixed methyl/methylidene precursors such as [Cp'(3)Ln(3)(μ(2)-Me)(3)(μ(3)-Me)(μ(3)-CH(2))] (3-Ln). The reaction of the methylidene complex 4-Lu with benzophenone leads to C═O bond cleavage and C═C bond formation to give the cubane-type oxo complex [Cp'Lu(μ(3)-O)](4) and CH(2)═CPh(2), while the methyl/methylidene complex 3-Tm undergoes sequential methylidene addition to the C═O group and ortho C-H activation of the two phenyl groups of benzophenone to afford the bis(benzo-1,2-diyl)ethoxy-chelated trinuclear complex [Cp'(3)Tm(3)(μ(2)-Me)(3){(C(6)H(4))(2)C(O)Me}] (6-Tm).     

Reactivity of the inversely polarized phosphaalkenes RP=C(NMe2)2 (R = tBu, Me3Si, H) towards arylcarbene complexes [(CO)5M=C(oEt)Ar] (Ar= Ph, M = Cr, W; Ar = 2-MeC6H4, 2-MeOC6H4, M = W)

The reaction of the arylated Fischer carbene complexes [(CO)5M=C(OEt)Ar] (Ar=Ph; M = Cr, W; 2-MeC6H4; 2-MeOC6H; M = W) with the phosphaalkenes RP=C(NMe2), (R=tBu, SiMe3) afforded the novel phosphaalkene complexes [[RP=C(OEt)Ar]M(CO)5] in addition to the compounds [(RP=C(NMe2)2]M(CO)5]. Only in the case of the R = SiMe3 (E/Z) mixtures of the metathesis products were obtained. The bis(dimethylamino)methylene unit of the phosphaalkene precursor was incorporated in olefins of the type (Me2N)2C=C(OEt)(Ar). Treatment of [(CO)5W=C(OEt)(2-MeOC6H4)] with HP=C(NMe2)2 gave rise to the formation of an E/Z mixture of [[(Me2N)2CH-P=C(OEt)(2-MeOC6H4)]W(CO)5] the organophosphorus ligand of which formally results from a combination of the carbene ligand and the phosphanediyl [P-CH(NMe2)2]. The reactions reported here strongly depend on an inverse distribution of alpha-electron density in the phosphaalkene precursors (Pdelta Cdelta+), which renders these molecules powerfu] nucleophiles.     

Synthetic and structural studies of donor-functionalized alkoxy derivatives of gallium

The synthesis of a range of alkyl/chloro-gallium alkoxide and amido/alkoxide compounds was achieved via a series of protonolysis and alcoholysis steps. The initial reaction involved the synthesis of [Me(Cl)Ga{N(SiMe(3))(2)}](2) (1) via methyl group transfer from the reaction of GaCl(3) with two equivalents of LiN(SiMe(3))(2). Reaction of 1 with varying amounts of ROH resulted in the formation of [Me(Cl)Ga(OR)](2) (2, R = CH(2)CH(2)OMe; 3, CH(CH(3))CH(2)NMe(2)), [Me(Cl)Ga{N(SiMe(3))(2)}(μ(2)-OR)Ga(Cl)Me] (4, R = CH(2)CH(2)NMe(2)), or [MeGa(OR)(2)] (5, R = CH(CH(3))CH(2)NMe(2)). Compound 4 represents an intermediate in the formation of dimeric complexes, of the type [Me(Cl)Ga(OR)](2), when formed from compound [Me(Cl)Ga{N(SiMe(3))(2)}](2). A methylgallium amido/alkoxide complex [MeGa{N(SiMe(3))(2)}(OCH(2)CH(2)OMe)](2) (6) was isolated when 2 was further reacted with LiN(SiMe(3))(2). In addition, reaction of 2 with HO(t)Bu resulted in a simple alcohol/alkoxide exchange and formation of [Me(Cl)Ga(O(t)Bu)](2) (7). In contrast to the formation of 1, the in situ reaction of GaCl(3) with one equivalent of LiN(SiMe(3))(2) yielded [Cl(2)Ga{N(SiMe(3))(2)}](2) in low yield, where no methyl group transfer has occurred. Reaction of alcohol with [Cl(2)Ga{N(SiMe(3))(2)}](2) was then found to yield [Cl(2)Ga(OR)](2) (8, R = CH(2)CH(2)NMe(2)), and further reaction of 8 with LiN(SiMe(3))(2) yielded the gallium amido alkoxide complex, [ClGa{N(SiMe(3))(2)}(OR)](2) (9, R = CH(2)CH(2)NMe(2)), similar to 6. The structures of compounds 4, 5, 7, and 8 have been determined by single-crystal X-ray diffraction.     

Intramolecular hydrophosphination/cyclization of phosphinoalkenes and phosphinoalkynes catalyzed by organolanthanides: scope, selectivity, and mechanism

Organolanthanide complexes of the general type Cp'(2)LnE(TMS)(2) (Cp' = eta(5)-Me(5)C(5); Ln = La, Sm, Y, Lu; E = CH, N; TMS = SiMe(3)) serve as effective precatalysts for the rapid intramolecular hydrophosphination/cyclization of the phosphinoalkenes and phosphinoalkynes RHP(CH(2))(n)()CH=CH(2) (R = Ph, H; n = 3, 4) and H(2)P(CH(2))(n)C triple bond C-Ph (n = 3, 4) to afford the corresponding heterocycles and respectively. Kinetic and mechanistic data for these processes exhibit parallels to, as well as distinct differences from, organolanthanide-mediated intramolecular hydroamination/cyclizations. The turnover-limiting step of the present catalytic cycle is insertion of the carbon-carbon unsaturation into the Ln-P bond, followed by rapid protonolysis of the resulting Ln-C linkage. The rate law is first-order in [catalyst] and zero-order in [substrate] over approximately one half-life, with inhibition by heterocyclic product intruding at higher conversions. The catalyst resting state is likely a lanthanocene phosphine-phosphido complex, and dimeric [Cp'(2)YP(H)Ph](2) was isolated and cystallographically characterized. Lanthanide identity and ancillary ligand structure effects on rate and selectivity vary with substrate unsaturation: larger metal ions and more open ligand systems lead to higher turnover frequencies for phosphinoalkynes, and intermediate-sized metal ions with Cp'(2) ligands lead to maximum turnover frequencies for phosphinoalkenes. Diastereoselectivity patterns also vary with substrate, lanthanide ion, and ancillary ligands. Similarities and differences in hydrophosphination vis-à-vis analogous organolanthanide-mediated hydroamination are enumerated.     

Synthesis, characterization and reactivity of new complexes of titanium and zirconium containing a potential tridentate amidinato-cyclopentadienyl ligand

Group 4 metal complexes [M(eta(5)-C(5)Me(4)SiMe(2)-eta(1)-N-2R)(NMe(2))(2)] (R = pyridine, pyrazine, pyrimidine, thiazole, M = Ti; R = pyridine, thiazole; M = Zr) containing the tetramethylcyclopentadienyl-dialkylsilyl bridged amidinato as pendant ligand, were synthesized and characterized by elemental analysis, solution (1)H, (13)C and (15)N NMR spectroscopy and experimental (13)C and (15)N CPMAS in the solid state. The crystal structures of [Ti(eta(5)-C(5)Me(4)SiMe(2)-eta(1)-N-2R)(NMe(2))(2)] (R = pyridine, pyrazine, pyrimidine, thiazole) were determined by single crystal X-ray diffraction studies. All compounds exhibit a distorted tetrahedral geometry, with the ansa-monocyclopentadienyl-amido ligands acting in a bidentate mode. The [M(eta(5)-C(5)Me(4)SiMe(2)-eta(1)-N-2R)(NMe(2))(2)] (R = pyridine, thiazole; M = Zr, Ti) complexes are ethylene polymerization catalysts in the presence of MAO and they are active precursors in regioselective catalytic hydroamination operating with an anti-Markovnikov mechanism.     

Homolysis of the Ln-N (Ln = Yb, Eu) bond. Synthesis, structural characterization and catalytic activity of ytterbium(II) and europium(II) complexes with methoxyethyl functionalized indenyl ligands

The interaction of methoxyethyl functionalized indene compounds (C(9)H(6)-1-R-3-CH(2)CH(2)OMe, R =t-BuNHSiMe(2)(1), Me(3)Si (2), H (3)) with [(Me(3)Si)(2)N](3)Ln(mu-Cl)Li(THF)(3)(Ln=Yb (4), Eu (5)) produced a series of new ytterbium(II) and europium(II) complexes via tandem silylamine elimination/homolysis of the Ln-N (Ln=Yb, Eu) bond. Treatment of the lanthanide(III) amides [(Me(3)Si)(2)N](3)Ln(mu-Cl)Li(THF)(3)(Ln=Yb (4), Eu (5) with 2 equiv. of, 1,2 and 3, respectively, produced, after workup, the ytterbium(II) complexes [eta5:eta1-Me(2)Si(MeOCH(2)CH(2)C(9)H(5))(NHBu-t)](2)Yb(II) (6), (eta5:eta1-MeOCH(2)CH(2)C(9)H(5)SiMe(3))(2)Yb(II) (7), (eta5:eta1-MeOCH(2)CH(2)C(9)H(6))(2)Yb(II)(8) and the corresponding europium(II) complexes [eta5:eta1-Me(2)Si(MeOCH(2)CH(2)C(9)H(5))(NHBu-t)](2)Eu(II)(9), (eta5:eta1-MeOCH(2)CH(2)C(9)H(5)SiMe(3))(2)Eu(II)(10) and (eta5:eta1-MeOCH(2)CH(2)C(9)H(6))(2)Eu(II)(11) in moderate to good yield. In contrast, interaction of the corresponding indene compounds 1, 2 or 3 with the lanthanide amides [(Me(3)Si)(2)N](3)Ln (Ln = Yb, Eu) was not observed, while addition of 0.5 equiv. of anhydrous LiCl to the corresponding reaction mixture produced, after workup, the corresponding ytterbium(II) or europium(II) complexes. All the new compounds were fully characterized by spectroscopic and elemental analyses. The structures of complexes, and were determined by single-crystal X-ray analyses. The catalytic activity of all the ytterbium(II) and europium(II) complexes on MMA polymerization was examined. It was found that all the ytterbium(II) and europium(II) complexes can function as single-component MMA polymerization catalysts. The temperature, solvent and ligand effects on the catalytic activity were studied.     

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.