Early-Transition-Metal Silyl Complexes Free from Anionic .pi.-Ligands. A New Family of Alkyl, Alkylidene, and Alkylidyne Compounds

Transition metal alkylidene complexes. Pathways in their formation and tautomerization between bis-alkylidenes and alkyl alkylidynes

“…Our initial interest was to study silyl alkylidene complexes (Me 3 ECH 2 ) 2 Ta(]CHEMe 3 )(SiR 3 ) (3a,b and 4a,b), silyl analogs of d 0 high-oxidation-state Schrock-type alkyl alkylidene [6,7,12,28,48], and to compare the silyl and alkyl complexes. These complexes were prepared by the reactions in Scheme 2.…”

“…These studies have been part of our investigations of early-transition-metal silyl, alkyl [43e49], and amide [50] complexes. The first part focuses on preparation of silyl alkylidene complexes (Me 3 ECH 2 ) 2 Ta(]CHEMe 3 )(SiR 3 ) [R 3 ¼ (SiMe 3 ) 3 , E ¼ C, 3a, Si, 3b; R 3 ¼ Bu t Ph 2 , E ¼ C, 4a, Si, 4b] [12,28] and studies of pathways in the formation of the silyl alkylidene (Me 3 SiCH 2 ) 2 Ta(]CHSiMe 3 )-[Si(SiMe 3 ) 3 ] (3b) [28] as well as alkyl alkylidenes (Me 3 ECH 2 ) 3 Ta] CHEMe 3 (E ¼ C, 5a; Si, 5b) [13,41]. The second part discusses the tautomerization of silyl alkylidyne (Me 3 CCH 2 ) 2 W(^CCMe 3 )(SiBu t Ph 2 ) (6a) with bis-alkylidene (Me 3 CCH 2 )W(]CHCMe 3 ) 2 (SiBu t Ph 2 ) (6b) [32,38] as well as (Me 3 SiCH 2 ) 3 W(^CSiMe 3 )(PR 3 ) [R 3 ¼ Me 3 , 7a; Me 2 Ph, 8a; Me 2 (CH 2 ) 2 PMe 2 (DMPE-P), 9a] with (Me 3 SiCH 2 ) 2 W(]CHSiMe 3 ) 2 (PR 3 ) (R 3 ¼ Me 3 , 7b; Me 2 Ph, 8b; DMPE-P, 9b) [P refers to a dangling P atom in Me 2 P(CH 2 ) 2 PMe 2 ] [37,39,42].…”

Reactivities of d0 transition metal complexes toward oxygen: Synthetic and mechanistic studies

“…This exchange is similar to the exchange Ta(NMe 2 ) 5 (6) + (Me 2 N) 3 Ta(ONMe 2 ) 2 (8) 2 (Me 2 N) 4 TaO-NMe 2 (7) discussed earlier [12] . Reactions of both (Me 2 N) 4 Ta(SiBu t Ph 2 ) (12) The −Si(SiMe 3 ) 3 group is bulkier than the −SiBu t Ph 2 group, and it may prevent the formation of additional products in the reaction of (Me 2 N) 3 TaSi(SiMe 3 ) 3 (11) with O 2 , yielding just one product [26][27][28][29][30][31][32][33][34][35][36] . In other words, kinetic barriers may have limited the reactivities of bulkier 11 and 12.…”

Unusual reaction of a tungsten alkylidyne complex with water. Formation, characterization, and crystal structures of oxo trimers

“…The two -H atoms in the neopentyl ligand are diastereotopic (-CH a H b CMe 3 ) [49]. However, only one doublet (H a ) is observed at room temperature, and the second doublet overlaps with the -CMe 3 resonance.…”

“…There is a mirror plane through W, Si, and the O atoms. The two -H atoms in the -CH 2 SiMe 3 ligands are equivalent; (b) a Newman projection of 4 showing that the two -H atoms in the -CH 2 CMe 3 ligands are diastereotopic[49].…”