Five-Coordinate Silicon(II) Compounds with Si-M Bonds (M = Cr, Mo, W, Fe): Bis[N,N′‑diisopropylbenzamidinato(-)]silicon(II) as a Ligand in Transition-Metal Complexes Konstantin Junold, † Johannes A. Baus, † Christian Burschka, † Thomas Vent-Schmidt, ‡ Sebastian Riedel,* ,‡,§ and Reinhold Tacke* ,† † Institut fü r Anorganische Chemie, Universitä t Wü rzburg, Am Hubland, 97074 Wü rzburg, Germany ‡ Institut fü r Anorganische und Analytische Chemie, Universitä t Freiburg, Albertstrasse 21, 79104 Freiburg im Breisgau, Germany § Institut fü r Chemie und Biochemie, Freie Universitä t Berlin, Fabeckstrasse 34-36, 14195 Berlin, Germany * S Supporting Information ABSTRACT: Reaction of the donor-stabilized silylene 1 with [Cr(CO) 6 ], [Mo(CO) 6 ], [W(CO) 6 ], or [Fe(CO) 5 ] leads to the formation of the transition-metal silylene complexes 2-5, which contain five-coordinate silicon(II) moieties with Si-M bonds (M = Cr, Mo, W, Fe). These compounds were characterized by NMR spectroscopic studies in the solid state and in solution and by crystal structure analyses. These experimental investigations were complemented by computa- tional studies to gain insight into the bonding situation of 2-5. The nature of the Si-M bonds is best described as a single bond. ■ INTRODUCTION The chemistry of stable silicon(II) compounds is currently one of the most actively studied fields in silicon chemistry. 1-4 Silicon(II) species (silylenes) show a very interesting reactivity profile; for example, they can behave as nucleophiles and therefore can act as ligands in transition-metal coordination chemistry. 5,6 In this context, stable N-heterocyclic silylene ligands play a special role. 1h Recently, we have reported the synthesis of bis[N,N′-diisopropylbenzamidinato(-)]silicon(II) (1), a novel stable donor-stabilized three-coordinate silylene, and its nucleophilic substitution reaction with [W(CO) 6 ] to form the tungsten silylene complex 4, in which the silicon atom is five-coordinate. 4n In continuation of these studies, we have now synthesized and characterized a series of further transition- metal complexes that also contain this particular silylene ligand, compounds 2, 3, and 5. In addition, we have performed computational studies to gain some insight into the bonding situation of compounds 2-5. Herein we report (i) the synthesis and structural character- ization of 2, 3, and 5, (ii) the synthesis of 4 4n using a slightly modified method, and (iii) the computational characterization of the electronic structure of 2-5. These investigations were performed as part of our systematic studies on higher- coordinate silicon(II) and silicon(IV) compounds (for recent publications, see refs 4n,o, and 6). ■ RESULTS AND DISCUSSION Syntheses. Compounds 2-5 were synthesized by reaction of 1 with [Cr(CO) 6 ], [Mo(CO) 6 ], [W(CO) 6 ], or [Fe(CO) 5 ] at 20 °C(2, 4, 5) or 60 °C(3) in toluene (2, 5) or THF (3, 4) (Scheme 1; yields (2) 76%, (3) 89%, (4) 92%, (5) 65%). Compounds 2-4 were isolated as colorless crystalline solids, whereas 5 was obtained as a green-colored crystalline product. The identities of 2-5 were established by elemental analyses, NMR spectroscopic studies in the solid state ( 15 N, 29 Si) and in solution ( 1 H, 13 C, 29 Si), and crystal structure analyses (for the crystal structure analysis of 4, see ref 4n). The formation of 2-5 can be described as a nucleophilic substitution reaction, in which the silylene 1 formally reacts as a four-coordinate nucleophile that replaces one of the six (Cr, Mo, W) or five (Fe) carbonyl groups to give a five-coordinate silicon(II) species with an M-Si bond (M = Cr, Mo, W, Fe). Crystal Structure Analyses. Compounds 2, 3, and 5 were structurally characterized by single-crystal X-ray diffraction. The crystal data and experimental parameters used for the crystal structure analyses are given in the Supporting Information (Table S1). The molecular structures of 2, 3, and 5 are depicted Received: July 30, 2013 Published: September 24, 2013 Article pubs.acs.org/IC © 2013 American Chemical Society 11593 dx.doi.org/10.1021/ic401954e | Inorg. Chem. 2013, 52, 11593-11599