This contribution describes lutetium and yttrium hydrocarbyl and hydride chemistry based upon the chelating R2Si(eta-5-C5H4)(eta-5-Me4C5)2- ligand (R = Me, Et; abbreviated R2SiCpCp''). The ligand is prepared by reaction of the corresponding R2Si(Cp'')Cl derivative with NaC5H5. Subsequent metalation and reaction with Mcl3.3THF (M = Y, Lu) yields R2SiCpCp''MCl2-Li(OEt2)2+ complexes, which in turn can be alkylated to yield R2SiCpCp''MCHTMS2 derivatives (TMS = SiMe3). Pertinent crystallographic data for Me2SiCpCp''LuCHTMS2 at -120-degrees-C: P(lbar) (no. 2), z = 4, a = 16.049 (3) angstrom, b = 17.945 (4) angstrom, c = 8.993 (c) angstrom, alpha = 93.36 (2) degrees, beta = 90.92 (2) degrees, and gamma = 92.54 (2) degrees; R(F) = 0.030 for 6085 independent reflections with 1 > 3-sigma(I). The structure is of a ''bent-sandwich'' Cp'2MX-type (Cp' = eta-5-Me5C5) with relaxed interligand nonbonded interactions vis-a-vis the Cp'2M and Me2SiCp''2M analogues (Lu-CHTMS2 = 2.365 (7) angstrom) and having one close Lu...MeSi (Lu-C = 2.820 (8) angstrom) secondary interaction. These alkyls initiate the polymerization of ethylene and undergo relatively slow hydrogenolysis to yield dihydrides of stoichiometry (R2SiCpCp''MH)2 via detectable intermediate of stoichiometry (R2SiCpCp'')2M2(H)(CHTmS2). Pertinent crystallographic data for (Et2SiCpCp''LuH)2 at 120-degrees-C: P2(1)/n (no. 14), z = 2, a = 11.558 (3) angstrom, b - 8.590 (2) angstrom, c = 18.029 (3) angstrom, beta = 100.10 (2) angstrom, R(F) = 0.022 for 2656 independent reflections with 1 > 3-sigma(I). The structure has an idealized C2h,Lu(mu-Et2SiCpCp'')2(mu-H)2Lu geometry with both bridging Et2SiCpCp'' and hydride ligands (Lu-H = 2.16 (4), 2.13 (4) angstrom). These complexes react slowly (compared to monomeric Cp'2MH and Me2SiCp''2MH), reversibly, and regiospecifically with alpha-olefins to form bridging alkyls of structure M(mu-R2SiCpCp'')2(mu-H)(mu-R')M,R' = ethyl, n-propyl, n-hexyl. Pertinent crystallographic data for Lu(mu-Et2SiCpCp'')2(mu-H)(mu-CH2CH3)Lu at -120-degrees-C: P2(1)/c (no. 14), z = 6, a = 11.679 (4) angstrom, b = 25.755 (5) angstrom, c = 18.074 (2) angstrom, beta = 99.41 (2) degrees; R(F) = 0.058 for 4643 independent reflections with 1 > 3-sigma(I). The Lu(mu-Et2SiCpCp'')2(mu-H)Lu framework is nearly identical to that in the dihydride above. The mu-ethyl fragment is bound very unsymmetrically with Lu-C(alpha) = 2.46 (2) and 2.58 (2) angstrom, < Lu-C(alpha)-C(beta) = 148 (1) degrees and 84.7 (5) degrees. In addition, Lu-C(beta) = 2.78 (2) angstrom suggests a strong secondary bonding interaction. Hydrogenolysis of the mu-alkyl linkages is considerably slower than for terminal alkyl bonds in Cp'2M(alkyl) and Me2SiCp''2M(alkyl) complexes. NMR studies of the mu-alkyls reveal rapid rotation of the mu-alkyl ligands about the mu-H-mu-C(alpha) vectors down to -85-degrees-C and rapid inversion at C(alpha) occurring with DELTA-G = 12.5-13.5 kcal/mol (T(c) = +11 = +39-degrees-C). Kinetic (rate law: v = k[dihydride][olefin]) and equilibration measurements reveal that the hydride additoin process to 1-hexene (Et2SiCpCp''LuH)2 + 1-hexene reversible Ky(mu-Et2SiCpCp)2(mu-H)(mu-n-hexyl)Lu is described by DELTA-H = 10.7 (6) kcal/mol, DELTA-S = -25 (2) eu, DELTA-H = 12.0 (4) kcal/mol, and DELTA-S = -38.6 (7) eu. These results indicate that, in comparison to terminal bonding modes with similar metal ancillary ligation, lanthanide mu-H ligands are kinetically deactivated with respect to olefin insertion (a rate depression of approximately 10(8)-10(10)), and mu-alkyl ligands are kinetically deactivated with respect to hydrogenolysis (a rate depression of approximately (10(8)-10(9)). Moreover, relative to a bridging hydride ligand, lanthanide mu-alkyl coordination is found to be no more and probably less thermodynamically stable than terminal alkyl coordination.
