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 NiCl 2 (DME) and N i Pr 2 Et afforded [( i Pr 2 EtNH) 2 Cl][(QnH)NiCl 3 ] ( 3; Qn = quinolyl) via degradation of the silane. Reaction of 2 with Ni(COD) 2 in chlorobenzene yielded [Ph-NSiN] 2 Ni 3 Cl 2 ( 5 ), which is a rare example of a silylnickel cluster with a [Ni 3 Si 2 ] core. An X-ray structure determination reveals the presence of a triangular Ni 3 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 Ni 3 skeletal orbital. Complex 5 slowly decomposes in dichloromethane- d 2 to (PhClSiQn 2 )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 η 2 -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 η 2 -coordination of the arene was estimated at the second-order donor−acceptor NBO level to be 25 kcal/mol.