Nickel Complexes with Bis(8-quinolyl)silyl Ligands. An Unusual Ni₃Si₂ Cluster Containing Six-Coordinate Silicon

Efforts to install the bis(8-quinolyl)methylsilyl (Me-NSiN; 1 = Me-NSiNH) and bis(8-quinolyl)phenylsilyl (Ph-NSiN; 2 = Ph-NSiNH) ligands onto nickel are described. Reaction of 1 with NiCl2(DME) and NiPr2Et afforded [(iPr2EtNH)2Cl][(QnH)NiCl3] (3; Qn = quinolyl) via degradation of the silane. Reaction of 2 with Ni(COD)2 in chlorobenzene yielded [Ph-NSiN]2Ni3Cl2 (5), which is a rare example of a silylnickel cluster with a [Ni3Si2] core. An X-ray structure determination reveals the presence of a triangular Ni3 core with two face-capping silyl groups: one that is bonded symmetrically to the three nickel atoms, while the other is unsymmetrically bound. The bonding in 5 has been investigated by computational methods to obtain descriptions of the molecular orbitals. The unsymmetrical bonding of Si(1) results from a two-electron bonding interaction with Ni(1), and this explains the short Si(1)−Ni(1) contact (2.2688(6) Å). The symmetrical bonding of Si(2) appears to result from its interaction with a delocalized Ni3 skeletal orbital. Complex 5 slowly decomposes in dichloromethane-d2 to (PhClSiQn2)NiCl (6), a Ni(I) chloride complex in which the phenyl group is bonded to the nickel with an intramolecularly coordinated (silyl)arene ligand. The η2-coordination of the aryl group involves interaction of ipso and ortho carbon atoms with the metal center. Theoretical studies of 6 support a very weak Ni−Si interaction (2−3 kcal/mol at the NBO level) that is supported by the arene coordination. The strength of the η2-coordination of the arene was estimated at the second-order donor−acceptor NBO level to be 25 kcal/mol.