INSERTION AND C-H BOND ACTIVATION OF UNSATURATED SUBSTRATES BY BIS(BENZAMIDINATO)YTTRIUM ALKYL, [PHC(NSIME(3))(2)](2)YR (R=CH(2)PH-CENTER-DOT-THF,CH(SIME(3))(2)), AND HYDRIDE, ([PHC(NSIME(3))(2)]Y-2(MU-H))(2),COMPOUNDS

The reactivity of benzamidinate-stabilized yttrium complexes [PhC(NSiM e(3))(2)](2)YR (R = CH(2)Ph . THF, CH(SiMe(3))(2) and {[PhC(NSiMe(3))( 2)]Y-2(mu-H)}(2) have been investigated. The complexes are thermally s table showing no sign of decomposition, ligand or solvent metalation o r H/D exchange after hours of 100 degrees C in cyclohexane-d(12) or be nzene-d(6). The alkyls are also stable in ethereal solvents. However, {[PhC(NSiMe(3))(2)]Y-2(mu-H)}(2) induces C-O cleavage in THF solutions . The complexes [PhC(NSiMe(3))(2)](2)YCH(2)Ph . THF and {[PhC(NSiMe(3) )(2)]Y-2(mu-H)}(2) are modestly active in ethylene polymerization but are inactive toward propylene and 1-hexene. Terminal alkynes react sto ichiometrically with [PhC(NSiMe(3))(2)]2YCH(SiMe(3))(2) and {[PhC(NSiM e(3))(2)]Y-2(mu-H)}(2) to give mu-acetylide dimers, {{PhC(NSiMe(3))(2) ]Y-2(mu-C=CR)}(2) (1, R = H; 2, R = Me; 3, R = n-Pr, 4, R = SiMe(3); 5 , R = Ph; 6, R = CMe(3)). Treatment with THF leads to cleavage of thes e dimers, yielding [PhC(NSiMe(3))(2)]2YC=Cr . THF (7, R = H; 8, R = CM e(3)). [PhC(NSiMe(3))(2)]Y-2(mu-Me)(2)Li . TMEDA reacts with HC=CCMe(3 ) to afford [PhC(NSiMe(3))(2)]Y-2(mu-C=CCMe(3))(2)Li . TMEDA. [PhC(NSi Me(3))(2)]2YCH(SiMe(3))(2) catalyzes the regioselective dimerization o f bulky 1-alkynes. With small 1-alkynes, HC=CR (R = H, Me, n-Pr), no d imerization was observed and the reaction stops with the formation of the alkynyl dimers {PhC(NSiMe(3))(2)]Y-2(mu-C=CR)}(2) (1-3). Treatment of [PhC(NSiMe(3))(2)](2)YR with acetonitrile gives either C-H bond ac tivation or insertion. For R = CH(SiMe(3))(2), C-H bond activation occ urs, yielding (NSiMe(3))(2)]Y-2(mu-(N,N')-N(H)C(Me)=C(H)C=N)}(2) (10). For R = CH(2)Ph . THF a mixture of C-H bond activation (10, 10%) and insertion products, {[PhC(NSiMe(3))(2)]Y-2(mu-N=C(Me)CH(2)Ph)}(2) (11a , 50%) and {[PhC(NSiMe(3))(2)]Y-2(mu-N(H)C(Me)=C(H)Ph)}(2) (11b, 40%), was obtained. The hydride {[PhC(NSiMe(3))(2)]Y-2(mu-H)}(2) exclusivel y gives insertion of acetonitrile, affording {[PhC(NSiMe(3))(2)]Y-2(mu -N=C(H)Me)}(2) (12). With pyridine, [PhC(NSiMe(3))(2)]2YCH(SiMe(3))(2) gives C-H bond activation, whereas [PhC(NSiMe(3))(2)](2)YCH(2)Ph . TH F and {[PhC(NSiMe(3))(2)]Y-2(mu-H)}(2) undergo insertion yielding [PhC (NSiMe(3))(2)]Y-2(NC(5)H(5)R) (13, R = H; 14, R = CH(2)Ph). In contras t with alpha-picoline, [PhC(NSiMe(3))(2)](2)YR (R = CH(SiMe(3))(2), Ch (2)Ph . THF) and {[PhC(NSiMe(3))(2)]Y-2(mu-H)}(2) afford the alpha-pic olyl derivative, [PhC(NSiMe(3))(2)]Y-2(eta(2)-(C,N)-2-CH2NC5H4 (15). T he difference in reactivity of the bis(benzamidinate)-stabilized compl exes compared to the corresponding Cp(2)YR systems, e.g. the low tend ency to catalyze C-C bond formation, the reduced or even the absence o f C-H/C-O activation properties, and the enhanced nucleophilic and Bro nsted base reactivities, is interpreted in terms of the high ionicity of the benzamidinate-stabilized yttrium complexes. The contracted yttr ium orbitals are less exposed than in the dicyclopentadienyl derivativ es and therefore not suited to establish the first initiating interact ion with substrate molecules.