The Direct Synthesis of a Silene–Organometallic Complex

Abstract

Dedicated to Professor Henry F. Schaefer III on the occasion of his 60th birthdayThe first stable compounds with doubly bonded silicon atoms were reported in 1981 and since then vast progress has been made in this field, [1] including the synthesis of several transition-metal complexes of silenes and disilenes such as compounds 1-4.[2-6] However, while numerous olefin-organometallic complexes were synthesized directly from the corresponding olefins, all known silene complexes were synthesized by indirect processes. For example, 1,[3] 2 a, [4] 2 b, [5] 3, [6] 4 a and 4 b [7a,b] were all obtained by cyclization reactions. Only 4 c was synthesized by a direct reaction of a disilene with an organometallic reagent, but its molecular structure was not determined by X-ray crystallography (Mes = C 6 H 2 Me 3 ).[7b]We report herein the synthesis and the molecular and electronic structure of a novel platinum h 2 -silene complex, 5, the first silene complex synthesized by a direct reaction of a silene (6) and an organometallic reagent Pt(PCy 3 ) 2 .Our initial attempts to obtain a silene-platinum complex by a reaction of Pt(PCy 3 ) 2 [8] and the stable silenes 7[9] and 8 [10] failed, thus leading to a complex mixture of products. Molecular models reveal that the double bond in 7 and 8 is so effectively protected by the very bulky R 1 and R 2

Isolable silylene, disilenes, trisilaallene, and related compounds

“…At the 13th International Symposium on Organosilicon Chemistry in Mexico in 2002, Prof. Apeloig informed in his lecture that the 14-electron platinum complex of stable silene was prepared by the reaction of bis(tricyclohexylphosphine)platinum with a stable silene [35]. In search of a disilene-transition metal p complex, the reaction of bis(tricyclohexylphosphine)palladium dichloride with dilithiodisilane 12b was investigated.…”

A Stable Silene Substituted by Strong π‐Donors at the Silicon Center

“…Indeed, similar structural data were observed in the case of the previously reported h 2 -silene-Pt 0 complex (Si À C: 1.838 , AE Si 8 = 3538), which presents a hybrid structure between p-complex and s-bonded compound. [23] In contrast, silene-Pt 0 complex 11 presents a higher p-complex character ( Figure 5). [12] Indeed, the Pt-silene distances are quite long (Si1ÀPt 2.440 , C1ÀPt 2.236 ) and the Si1ÀC1 bond length remains relatively short (1.802 ) compared to those observed in the related complex with a PCy 3 ligand.…”

“…It is worth noting that this is the first example of a direct synthesis of silenetransition metal complexes involving a stable and isolable silene ligand. [23] The X-ray diffraction analysis of silene-Ni 0 complex 10 reveals a dimeric structure involving the h 6 -coordination of the phenyl groups to the Ni centers ( Figure 4). The exocyclic SiC bond (1.825 ) is considerably elongated compared to free ligand 2 (1.725 ), and the silicon center is strongly pyramidalized (AE Si 8 = 343.68).…”

“…[12] Indeed, the Pt-silene distances are quite long (Si1ÀPt 2.440 , C1ÀPt 2.236 ) and the Si1ÀC1 bond length remains relatively short (1.802 ) compared to those observed in the related complex with a PCy 3 ligand. [23] This different bonding situation could be attributed to the presence in 11 of an electron-withdrawing vinyldisiloxane ligand on Pt, instead of a strong electron-donating phosphine ligand, which decreases the p-back-donation from the metal to the silene ligand.…”

5 Carbon, silicon, germanium, tin and lead

“…The structural studies indicate a structure that is predictably intermediate between a p-bound silylene and a formal cyclopropane. 114 Another very exciting result covered in this section this year comes from the reaction of Pt(PPh 3 ) 4 with the Zintl ion Pb 9 42 in the presence of ethylenediamine which gives the extraordinary [Pt@Pb 12 ] 22 . This fascinating compound, readily prepared from an amazingly simple reaction, comprises a regular dodecaplumbane with a platinum contained within.…”