Access to Silicon(II)- and Germanium(II)-Indium Compounds Sanjukta Pahar, †,‡ Suvendu Karak, ‡,§ Moumita Pait, † K. Vipin Raj, § Kumar Vanka, ‡,§ and Sakya S. Sen* ,†,‡ † Inorganic Chemistry and Catalysis Division, CSIR-National Chemical Laboratory, Dr. Homi Bhabha Road, Pashan, Pune 411008, India ‡ Academy of Scientific and Innovative Research (AcSIR), New Delhi 110020, India § Physical and Material Chemistry Division, CSIR-National Chemical Laboratory, Dr. Homi Bhabha Road, Pashan, Pune 411008, India * S Supporting Information ABSTRACT: Despite the remarkable ability of N-heterocyclic silylene to act as a Lewis base and form stable Lewis adducts with group 13 elements such as boron, aluminum, and gallium, there has been no such comparable investigation with indium and the realization of a stable silylene-indium complex has still remained elusive. Similarly, a germylene-indium complex is also presently unknown. We describe herein the reactions of [PhC(NtBu) 2 SiN- (SiMe 3 ) 2 ](1) and [PhC(NtBu) 2 GeN(SiMe 3 ) 2 ](4) with InCl 3 and InBr 3 that have resulted in the first silylene-indium complexes, [PhC(NtBu) 2 Si{N(SiMe 3 ) 2 }→InCl 3 ](2) and [PhC(NtBu) 2 Si{N(SiMe 3 ) 2 }→InBr 3 ](3), as well as the first germylene-indium complexes, [PhC(NtBu) 2 Ge{N(SiMe 3 ) 2 }→InCl 3 ](5) and [PhC(NtBu) 2 Ge{N(SiMe 3 ) 2 }→InBr 3 ](6). The solid-state structures of all species have been validated by single-crystal X-ray diffraction studies. Note that 5 and 6 are the first structurally characterized organometallic compounds that feature a Ge-In single bond (apart from the compounds in Zintl phases). Theoretical calculations reveal that the Si(II)→In bonds in 2 and 3 and the Ge(II)→In bonds in 5 and 6 are dative bonds. ■ INTRODUCTION The concept of chemical bonding that the combination of a Lewis base and a Lewis acid results in the formation of a Lewis adduct has just celebrated its centenary anniversary 1 and is still growing stronger. With the advent of stable N-heterocyclic carbenes (NHCs) and their higher homologues, N-heterocyclic silylenes (NHSis), we have entered into a new era of neutral Lewis bases. The realization of NHC and NHSi complexes of main-group elements has seen a flurry of research activity into their bonding properties and reactivity in recent years. 2,3 However, there are a few main-group halides for which the coordination chemistry of NHC and NHSi either has been explored only cursorily or has not been developed at all. Indium halide is one prominent example of such a halide. In fact, the organometallic chemistry of indium is, by far, significantly less developed in comparison to its lighter congeners such as boron, aluminum, and gallium. This is partially due to the low solubility of indium halides in a majority of organic solvents. Nevertheless, on adoption of a salt elimination methodology between InCl 3 and lithiated ligands, quite a few indium derivatives have been isolated. 4 Very recently, Braunschweig and co-workers reported the formation of a metal-only Lewis pair (MOLP) 5 between indium halides and electron-rich coordinatively unsaturated zerovalent platinum compounds. 6 They have also demonstrated that a dynamic equilibrium exists between MOLPs and their oxidative addition products. 6 The N-heterocyclic carbene (NHC) chemistry of indium has also come to the fore in recent years. The advances made in this field have mainly come from the group of Jones and co-workers, who isolated coordination complexes between NHC and indium halides. 7a,b Subsequently, their trimethyl complexes with NHCs have also been realized. 7c Thorough quantum mechanical calculations on the structures and stabilities of NHC-indium adducts have also been reported. 8 The use of indium compounds in electronics (indium is becoming one of the most important dopant species for silicon crystals used in photovoltaics, for instance) 9 has provided renewed interest in the chemistry of silicon and indium. Early works by Gö tze, 10 Cowley, 11 Weidlein, 12 and, to a large extent, by Wiberg 13 have led to the isolation of a variety of silyl-indium compounds, where the formal oxidation state of silicon is +4. However, in recent years, attention has shifted to silicon compounds, where the formal oxidation state of silicon is +2, popularly known as silylenes. 14 Examples of carbonyl-free silylene complexes of 3d transition metals in the formal oxidation state +2 are now too frequent to be comprehensively listed, thanks to extensive investigations by the groups of H. Roesky, P. Roesky, Stalke, Driess, Tacke, Inoue, Khan, and many others. 15-26 The coverage of the s and p blocks is also expanding Received: February 13, 2018 Article Cite This: Organometallics XXXX, XXX, XXX-XXX © XXXX American Chemical Society A DOI: 10.1021/acs.organomet.8b00093 Organometallics XXXX, XXX, XXX-XXX