Synthesis and Characterization of Thermally Robust Amidinato Group 13 Hydride Complexes

Abstract

The reactivity of two sterically bulky amidines, ArNC(R)N(H)Ar (Ar=2,6-diisopropylphenyl; R=H (HFiso); tBu, (HPiso)) towards LiMH4, M=Al or Ga, [AlH3(NMe3)], and [GaH3(quin)] (quin=quinuclidine) has been examined. This has given rise to a variety of very thermally stable aluminum and gallium hydride complexes. The structural motif adopted by the prepared complexes has been found to be dependent upon both the amidinate ligand and the metal involved. The 1:1 reaction of HFiso with LiAlH4 yielded dimeric [{AlH3(mu-Fiso)Li(OEt2)}2]. Amidine HFiso reacts in a 1:1 ratio with [AlH3(NMe3)] to give the unusual hydride-bridging dimeric complex, [{AlH2(Fiso)}2], in which the Fiso- ligand is nonchelating. The equivalent reaction with the bulkier amidine, HPiso, yielded a related hydride-bridging complex, [{AlH2(Piso)}2], in which the Piso- ligand is chelating. In contrast, the treatment of [GaH3(quin)] with one equivalent of HFiso afforded the four-coordinate complex [GaH2(quin)(Fiso)], in which the Fiso- ligand acts as a localized monodentate amido-imine ligand. The 2:1 reactions of HFiso with [AlH3(NMe3)] or [GaH3(quin)] gave the monomeric complexes [MH(Fiso)2], which are thermally robust and which exhibit chelating amidinate ligands. In contrast, HPiso did not give 2:1 complexes in its reactions with either of the Group 13 trihydride precursors. For sake of comparison, the reactions of [AlH3(NMe3)] and [GaH3(quin)] with the bulky carbodiimide ArN=C=NAr and the thiourea Ar(H)NC(=S)N(H)Ar were examined. These last reactions afforded the five-coordinate thioureido complexes, [MH{N(Ar)C[N(H)(Ar)]S}2], M=Al or Ga.

Aluminum and Indium Complexes derived from Guanidines, Triazenes, and Amidines

“…The relative stabilities of these depend on the steric bulk at the NCN/NNN unit, which, in addition to controlling nuclearity, affects the aluminohydride function in terms of electronic stabilization and geometric constraints. For example, the smaller Fiso amidinate (Figure 1) facilitates a paddle‐wheelesque amidinate bridged [{AlH(μ‐H)(μ‐Fiso)} 2 ] structure with an NCN angle of 122.0(5)° (dec. 205–207 °C) 11b. The related pivamidinate (Piso, Figure 1) cannot generate such a large NCN angle, leading to chelation in the related aluminum dihydride complex; [{AlH(Piso)(μ‐H)} 2 ] [NCN 107.3(2)°],11b,20 and N ‐2, 6‐dimesitylphenyl‐ N' ‐mesityltriazenide affords a monomeric, NNN‐chelated, aluminum dihydride 11d.…”

Synthesis, Electronic Properties, and Reactivity of Phospholes and 1,1′‐Biphospholes Bearing 2‐ or 3‐Thienyl C‐Substituents

“…In contrast, the monoanionic formamidinate in 2 coordinates to the K + ion in a η 1 ‐N,η 6 ‐arene mode. Because the structures of both ions 1 15 and 2 16 have been previously reported, they are not discussed here in detail 17…”

Oxidative Addition Reactions of Element–Hydrogen Bonds with Different Polarities to a Gallium(I) Compound

“…Compared to other gallium hydrides, this covers the whole known shift range. [21,22,30,[34][35][36][37] The trend in the series of compounds 2-6 shows a shift to lower frequencies with increasing electronegativity of X. Consequently, 2, with the electropositive tin atom connected to gallium, has the most deshielded Ga À H. Formally, the gallium atom has reversed polarity.…”