A Germanium Isocyanide Complex Featuring (n → π*) Back-Bonding and Its Conversion to a Hydride/Cyanide Product via C–H Bond Activation under Mild Conditions

Abstract

ABSTRACT:Reaction of the diarylgermylene, Ge(Ar Me 6) 2 (Ar Me 6 = C6H3-2,6-(C6H2-2,4,6-(CH3)3)2 with tertbutylisocyanide gave the Lewis adduct species, (Ar Me 6) 2GeCNBu t , in which the isocyanide ligand displays a decreased C-N stretching frequency consistent with an n -π* back-bonding interaction. Density functional theory confirms that the HOMO is a Ge-C bonding combination between the lone pair of electrons at the germanium atom and the C-N π* orbital of the isocyanide ligand. The complex undergoes facile C-H bond activation to produce a new diarylgermanium hydride/cyanide species and isobutene via heterolytic cleavage of the N-Bu t bond.Synergism is a central concept for the understanding of bonding in organometallic compounds -most notably in transition metal complexes of σ-donor/ π-acid ligands. Carbonyl (CO) and isocyanide (CNR) molecules are amongst the most widely studied ligands of this type, and the latter generally displays stronger σ-donor and weaker π-acceptor character than carbonyls. 1,2 In addition, whereas the C-O stretching frequency is always lowered upon complexation to a transition metal, the C-N frequency of an isocyanide can shift to higher as well as lower frequency. The shifts to higher frequency generally occur in transition metal complexes with a weak π-donating tendency toward the isocyanide and the M-C bond is dominated by σ effects. 2,3 Tetrylene -isocyanide complexes may be divided into two categories which are defined by two bonding extremes. The first involves multiple bonding between the isocyanide carbon and the main group element in which the isocyanide is subsumed into a heterocumulene structure. 4 The other example involves a simple donor -acceptor interaction between the carbon and main group atom -in other words a single σ bond. To date, the limited number of spectroscopically characterized stannylene and plumbylene -isocyanide complexes are Lewis adducts and display higher ν(CN) stretching frequencies than the free ligand, indicating primarily a σ donor bond with low or zero π-backbonding to the isocyanide. Silicon -isocyanide complexes tend to form heterocumulenes, however, when very bulky isocyanides are used, Lewis adducts have been isolated which exhibit ν(CN) stretching frequencies lower than that of the free ligand. 5 Although the possibility of π-back-bonding in these adducts has not been explored, there have been numerous recent reports of the activation of small molecules such as H2, NH3, or C2H4, via synergistic pathways in which a main group atom(s) behaves as both electron donor and acceptor. [6][7][8] We now report that the addition of tert-butylisocyanide to a diarylgermylene leads to the formation of a Lewis adduct, (Ar Me 6) 2GeCNBu t (1) [Ar Me 6 = C6H3-2,6-(C6H2-2,4,6-(CH3)3)2]. Further analysis of the metalisocyanide bonding mode in 1 by density functional theory (DFT) indicates that 1 displays back-bonding from the lone pair on germanium to the π* orbital of the isocyanide ligand. 9 The adduct, 1, also undergoes C-H activation with mild heating of...

Alkyne Addition and Insertion Reactions of [(Me3Si)3Si]2Ge⋅PMe3

“…Klinkhammer already reported reactions of bis[tris(trimethylsilyl)silyl]stannylene and plumbylene with tert‐ butylisocyanide and cyclohexylisocyanide to form stable adducts . Additionally, Power and co‐workers described the conversion of tert‐ butylisocyanide with a diarylgermylene, which underwent a subsequent decomposition step that involved C−H activation of the tert ‐butyl group and formation of isobutene and a germylnitrile …”

Germylene Cyanide Complex: A Reagent for the Activation of Aldehydes with Catalytic Significance

“…A signal at d = 139.2 ppm confirms the presence of a cyanide group. [14] In the IR spectrum of compound 2, a medium band at n = 2131 cm À1 further confirms the presence of the cyano group.…”

Activation of Isocyanides and Hydrosilanes by a Cationic [CCH] Subunit in a Tetrairon–Tetracarbon Cluster

“…22 Power et al reported the isolation and X-ray characterization of Ar 2 GeCN t Bu [Ar = C 6 H 3 -2,6-(C 6 H 2 -2,4,6-(CH 3 ) 3 ) 2 ], which was further converted to Ar 2 GeH(CN) and isobutene upon heating through heterolytic cleavage of the N t Bu bond. 23 Sekiguchi and Ichinohe reported the reaction of disilyne, RSi¸SiR (R = Si i Pr[CH(SiMe 3 ) 2 ] 2 ), with tert-butyl isocyanide to form a disilyneisocyanide adduct below ¹30°C. Warming the solution caused decomposition and produced 1,2-dicyanodisilene R(NC)Si=Si(CN)R and 1,2-dicyanodisilane R(NC)HSiSiH(CN)R together with isobutene and isobutane.…”