Homoleptic tris(alkyl) rare earth complexes Ln{C(SiHMe)} (Ln = La, 1a; Ce, 1b; Pr, 1c; Nd, 1d) are synthesized in high yield from LnITHF and 3 equiv of KC(SiHMe). X-ray diffraction studies reveal 1a-d are isostructural, pseudo-C-symmetric molecules that contain two secondary Ln↼HSi interactions per alkyl ligand (six total). Spectroscopic assignments are supported by comparison with Ln{C(SiDMe)} and DFT calculations. The Ln↼HSi and terminal SiH exchange rapidly on the NMR time scale at room temperature, but the two motifs are resolved at low temperature. Variable-temperature NMR studies provide activation parameters for the exchange process in 1a (ΔH = 8.2(4) kcal·mol; ΔS = -1(2) cal·molK) and 1a-d (ΔH = 7.7(3) kcal·mol; ΔS = -4(2) cal·molK). Comparisons of lineshapes, rate constants (k/k), and slopes of ln(k/T) vs 1/T plots for 1a and 1a-d reveal that an inverse isotope effect dominates at low temperature. DFT calculations identify four low-energy intermediates containing five β-Si-H⇀Ln and one γ-C-H⇀Ln. The calculations also suggest the pathway for Ln↼HSi/SiH exchange involves rotation of a single C(SiHMe) ligand that is coordinated to the Ln center through the Ln-C bond and one secondary interaction. These robust organometallic compounds persist in solution and in the solid state up to 80 °C, providing potential for their use in a range of synthetic applications. For example, reactions of Ln{C(SiHMe)} and ancillary proligands, such as bis-1,1-(4,4-dimethyl-2-oxazolinyl)ethane (HMeC(Ox)) give {MeC(Ox)}Ln{C(SiHMe)}, and reactions with disilazanes provide solvent-free lanthanoid tris(disilazides).

The organolanthanide complexes Ln{C(SiHMe 2) 3 } 3 (Ln = La, 1a; Ce, 1b; Pr, 1c; Nd, 1d) react with one or two equiv. of B(C 6 F 5) 3 to yield the well-defined zwitterionic species Ln{C(SiHMe 2) 3 } 2 HB(C 6 F 5) 3 (Ln = La, 2a; Ce, 2b; Pr, 2c; Nd, 2d) or LnC(SiHMe 2) 3 {HB(C 6 F 5) 3 } 2 (Ln = La, 3a; Ce, 3b; Pr, 3c; Nd, 3d), respectively. These complexes are shown to contain labile, bridging Si-H⇀Ln and oF ->Ln interactions based upon the observation of low one-bond silicon-hydrogen coupling constants (1 J SiH) in 1 H NMR spectra of 2a and 3a, the presence of one set of C 6 F 5 signals in the 19 F NMR spectra of 2a and 3a, the detection of only m-F and p-F resonances in 19 F NMR spectra of 2b-d and 3b-d, two ν SiH bands in IR spectra of 2a-d, and X-ray crystallography analyses of 2b and 3d. In addition, a hexametertoluene molecule is coordinated to neodymium in 3d. Reactions of 1a and (AlMe 3) 2 yield labile adducts with an approximate stoichiometry of 1a•3AlMe 3. Exchange between free and bound AlMe 3 groups was observed in EXSY NMR experiments with greater than 3 equiv. of AlMe 3. Compounds 2a-d and 3a-d, in the presence of AliBu 3 , are precatalysts for polymerization of butadiene. The neodymium alkyl 3d has the highest activity of the series, and its performance is consistent with chain transfer reactions with AliBu 3 .

A bulky, optically active monoanionic scorpionate ligand, tris(4S-isopropyl-5,5-dimethyl-2-oxazolinyl)phenylborate (ToP*), is synthesized from the naturally occurring amino acid l-valine as its lithium salt, Li[ToP*] (1). That compound is readily converted to the thallium complex Tl[ToP*] (2) and to the acid derivative H[ToP*] (3). Group 7 tricarbonyl complexes ToP*M(CO)3(M = Mn (4), Re (5)) are synthesized by the reaction of MBr(CO)5 and Li[ToP*] and are crystallographically characterized. The νCO bands in their infrared spectra indicate that π back-donation in the rhenium compounds is greater with ToP* than with non-methylated tris(4S-isopropyl-2-oxazolinyl)phenylborate (ToP). The reaction of H[ToP*] and ZnEt2 gives ToP*ZnEt (6), while ToP*ZnCl (7) is synthesized from Li[ToP*] and ZnCl2. The reaction of ToP*ZnCl and KOtBu followed by addition of PhSiH3 provides the zinc hydride complex ToP*ZnH (8). Compound 8 is the first example of a crystallographically characterized optically active zinc hydride. We tested its catalytic reactivity in the cross-dehydrocoupling of silanes and alcohols, which provided Si-chiral silanes with moderate enantioselectivity. Disciplines Chemistry CommentsReprinted (adapted) with permission from Organometallics 34 (2015) (5)) are synthesized by the reaction of MBr(CO) 5 and Li[To P *] and are crystallographically characterized. The ν CO bands in their infrared spectra indicate that π back-donation in the rhenium compounds is greater with To P * than with non-methylated tris(4S-isopropyl-2-oxazolinyl)phenylborate (To P ). The reaction of H[To P *] and ZnEt 2 gives To P *ZnEt (6), while To P *ZnCl (7) is synthesized from Li[To P *] and ZnCl 2 . The reaction of To P *ZnCl and KOtBu followed by addition of PhSiH 3 provides the zinc hydride complex To P *ZnH (8). Compound 8 is the first example of a crystallographically characterized optically active zinc hydride. We tested its catalytic reactivity in the cross-dehydrocoupling of silanes and alcohols, which provided Si-chiral silanes with moderate enantioselectivity.

Zwitterionic nickel(II) compounds with a borate-containing anionic bidentate phosphine ligand (PBP -) have been synthesized and some of them crystallographically characterized. The methyl complex, (PBP -)Ni + CH 3 (NCCH 3 ), reacts with H 2 to form an 12-membered macrocycle containing three Ni nuclei and reacts with carbon monoxide (CO) to afford the acetyl complex (PBP -)Ni + COCH 3 (CO). The square planar acetyl complex is stable in solution under one atmosphere of CO but undergoes irreversible decomposition under high CO pressure at room temperature. X-Ray crystallographic characterization of a decomposition product revealed fragmentation of the anionic borate under high pressure. (PBP -)Ni + COCH 3 (CO) is an active catalyst for ethylene-CO copolymerization, but its productivity is low likely due to its instability under high CO pressure.