Metal-metal bonded alkaline-earth distannyls

Mg(I)-Fe(-II) and Mg(0)-Mg(I) covalent bonding in the MgnFe(CO)4- (n = 1, 2) anion complexes: an infrared photodissociation spectroscopic and theoretical study

Heteronuclear magnesium-iron carbonyl anion complexes MgFe(CO)₄^- and Mg₂Fe(CO)₄^- are produced in the gas phase and are detected by mass-selected infrared photodissociation spectroscopy in the carbonyl stretching frequency region. The geometric structures and the metal-metal bonding are discussed with the aid of quantum chemical calculations. Both complexes are characterized to have a doublet electronic ground state with C_3v symmetry containing a Mg-Fe bond or a Mg-Mg-Fe bonding unit. Bonding analyses indicate that each complex involves an electron-sharing Mg(I)-Fe(-II) σ bond. The Mg₂Fe(CO)₄^- complex involves a relatively weak covalent Mg(0)-Mg(I) σ bond.

The structures of ring-expanded NHC supported copper(I) triphenylstannyls and their phenyl transfer reactivity towards heterocumulenes

Three ring-expanded N-heterocyclic carbene-supported copper(I) triphenylstannyls have been synthesised by the reaction of (RE-NHC)CuO^tBu with triphenylstannane (RE-NHC = 6-Mes, 6-Dipp, 7-Dipp). The compounds were characterised by NMR spectroscopy and X-ray crystallography. Reaction of (6-Mes)CuSnPh₃ with di-p-tolyl carbodiimide, phenyl isocyanate and phenylisothiocyanate gives access to a copper(I) benzamidinate, benzamide and benzothiamide respectively via phenyl transfer from the triphenylstannyl anion with concomitant formation of (Ph₂Sn)_n. Attempts to exploit this reactivity under a catalytic regime were hindered by rapid copper(I)-catalysed dismutation of Ph₃SnH to Ph₄Sn, various perphenylated tin oligomers, H₂ and a metallic material thought to be Sn(0). Mechanistic insight was provided by reaction monitoring via NMR spectroscopy and mass spectrometry.

Bonding analysis in ytterbium(II) distannyl and related tetryls

The syntheses of the ytterbium(II) distannyl [Yb{Sn(SiMe₃)₃}₂·(thf)₄] (Yb-Sn) and of its digermyl analogue [Yb{Ge(SiMe₃)₃}₂·(thf)₃] (Yb-Ge) are presented. The compounds were characterised by multinuclear high-resolution solution NMR spectroscopy, including ¹⁷¹Yb NMR, and by X-ray diffraction crystallography. The bonding and electronic properties of the two complexes, along with those of the known ytterbium(II) disilyl derivative [Yb{Si(SiMe₃)₃}₂·(thf)₃] (Yb-Si) and those of the congeneric calcium distannyl [Ca{Sn(SiMe₃)₃}₂·(thf)₄] (Ca-Sn), were investigated in detail by DFT calculations. This analysis points at a primarily ionic Yb-tetrel bonding, with a small covalent contribution, attributed principally to the 5d(Yb) participation. This weak covalent character is found to be larger for the distannyl Yb-Sn than for its lighter Si- and Ge-derivatives. The covalent component is also found to be greater in Yb-Sn than in Ca-Sn, due to the availability of the 5d(Yb) orbitals for bonding.