Bis(amidinate) Complexes of Silicon and Germanium

Abstract

The synthesis of novel bis(amidinate) silicon and germanium complexes is described. The reaction of two equiv. of [MeC(NiPr)2]Li · THF (1) with SiCl4, GeCl4 or GeCl2·dioxane affords [MeC(NiPr)2]2SiCl2 (2), [MeC(NiPr)2]2GeCl2 (3) and [MeC(NiPr)2]2Ge (4), respectively. The complexes 2 and 4 have been structurally characterized. The crystallographic results confirm a bidentate coordination of the amidinate ligands at the Si/Ge center, as indicated by spectroscopic studies.

Dimethyl-, diphenyl- and cyclotetramethylene silylchloride derivatives of guanidine, their synthesis and structure. Formation of pentacoordinated silicon compounds and an unexpected diionic disila-diguanidinium dichloride

“…The distortion from trigonal bipyrimidal geometry described as the distance of Si(1) from the plane of the equatorial substituents is 0.131 Å . Karsch et al [33] have reported Si-Cl bond lengths from 2.185 to 2.197 Å in k 6 Si-bis-amidine (6) and 2.007 to 2.032 Å in k 5 Si-amidine (7). In 3, the apical Si(1)-Cl(1) bond is lengthened to a value of 2.240 Å (Scheme 3).…”

“…We therefore looked at 4-ring k 5 Si-amidines as well as 5-ring k 5 Si and 4-ring k 6 Si-guanidine systems. The examples we found were a guanidine (5) by Kummer [32] together with a k 6 Si-bis-amidine (6) and k 5 Si-amidine (7) by Karsch [33][34][35] (Scheme 3).…”

“…The apical Si(1)-N(9) bond length in 3 is extended to a value of 1.978 Å and with the equatorial Si(1)-N(1) bond to 1.777 Å . Similar lengths were reported by Karsch in the k 6 Si-bis-amidine structure (6), where the Si-N bonds were 1.841-1.837 Å when the chelating nitrogenÕs were trans to each other, and Si-N bonds of 1.915-1.914 Å when trans to a Si-Cl bond [33]. The N(5)-C(10) bond length is 1.311(7) Å in 3 which is the shortest C-N bond length among compounds 2-4.…”

Dianionic amidinates at silicon and germanium centers: Four-, six- and eight-membered rings

“…To reduce this steric hindrance, we tested the same type of reaction at a somewhat bigger, but comparable coordination center: we replaced Si(IV) by Ge(II). Germanium (II) has been demonstrated to be a suitable coordination center for amidinates [2,4,[19][20][21]. And indeed, by reacting GeCl 2 AE dioxane with the then sterically unfavorable amidinate 1c, no addition of another base was required for deprotonation, due to spontaneous deprotonation by a second equivalent of 1c and 5c was obtained as colorless crystals from toluene (Eq.…”

“…The mass spectrum of 5c revealed the presence of a tetrameric compound {Ge[(NH) 2 ( t Bu)C(Ph)]} 4 , but no decision could be made about the true nature: either a cubane like structure [22] or a twisted eight-membered ring within a 16-membered macrocycle (there is a unique structural analogue in tin chemistry [23]) seemed most likely. (7), C20-N21-Ge1A 132.48 (19), C20-N21-Ge2 92.88(9), Ge1A-N21-Ge2 134.67 (7),…”