Synthesis of M^II[N(SiMe₃)₂][Me₃SiNC(^tBu)NSiMe₃] (M = Sn, Ge) from Amidinate Precursors:  Active Catalysts for Phenyl Isocyanate Cyclization

Abstract

Mixed amidinato amido complexes [Me3SiNC(tBu)NSiMe3]M[N(SiMe3)2] (M = Sn 2, Ge 3) were prepared by the reaction of [Me3SiNC(tBu)NSiMe3]Li (1a) with SnCl2 and GeCl2(dioxane) in ether. The N(SiMe3)2 ligand in these compounds is derived from the rearrangement of the [Me3SiNC(tBu)NSiMe3]- anion with extrusion of tBuCN. The susceptibility of [Me3SiNC(tBu)NSiMe3]- to rearrangement appears to be dependent on reaction solvent and on the coordinated metal center. Single-crystal X-ray diffraction studies of 2 and 3 are presented. Replacement of Me for tBu in the ligand allowed [Me3SiNC(Me)NSiMe3]2SnII (4) to be isolated, and an X-ray structure of this compound is reported. The isolation of 4 indicates that steric factors also play a role in the stability of [Me3SiNC(tBu)NSiMe3]-. Compounds 2 and 3 are outstanding catalysts for the cyclotrimerization of phenyl isocyanates to perhydro-1,3,5-triazine-2,4,6-triones (isocyanurates) at room temperature. In contrast, complex 4 catalytically reacts with phenyl isocyanate to produce isocyanate dimer and trimer in a 52:35 ratio.

New stable germylenes, stannylenes, and related compounds

“…However, it is much longer than those observed in previously studied amino-functionalized Ge(II) compounds of this type (2.092(3)-2.165(5) Å ) [3,12,19,20]. This value of the Ge N bond length in 1 may be due to some degree of p-bonding between germanium and nitrogen N (2) [22], but markedly shorter than that in the sterically strained ArGeN(SiMe 3 ) 2 (Ar = 2,6-bis((diethylamino)-methyl)phenyl) (1.956(1) Å ) [23].…”

Oxidative Additions of Homoleptic Tin(II) Amidinate

“…3a,e Only a rarely described oxidation product of tin(II) amidinates, the amidinatotin(IV) tetrasulfide 4 as well as its low valent precursors can initiate the catalytically driven cyclotrimerization of phenylisocyanates quite efficiently. 4,5 There are a couple of additional examples of the tin(II) amidinate oxidation by sulfur or diphenyldisulfide 6 leading to tin(IV) species with a cyclic structure 4 or a terminal Sn−S highly polarized double bond 3d reported by Richeson. From the same group, the description of the preparation and structure of the bisamidinatotin(IV) dichlorides appeared as well.…”

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.…”