High yield syntheses of neutral and cationic aminocarbyne complexes of
chromium-bearing isocyanide ligands are reported. Neutral complexes o
f the type Br(CO)(2)(RNC)(2)Cr=(CNPr2)-Pr-i(R = Et (3a); R = (t)Bu (3b
)) are obtained from Br(CO)(2)(pic)(2)Cr=(CNPr2)-Pr-i (2) (pic = gamma
-picoline) by exchange of the gamma-picoline ligands with RNC, Complex
3b reacts with (t)BuNC in toluene at 60 degrees C to give the monocar
bonyl derivative Br(CO)((t)BuNC)(3)Cr=(CNPr2)-Pr-i (4b). Formation of
cationic aminocarbyne complexes is favoured in polar solvents as demon
strated by the reaction of 3a or 3b with RNC in refluxing CH2Cl2 which
leads exclusively to [(RNC)(4)(CO)Cr=(CNPr2)-Pr-i]Br (R = Et (5a); R
= (t)Bu (5b)). Thermal decarbonylation of 5b with (t)BuNC in refluxing
tetrahydrofuran (THF) affords the cationic aminocarbyne complex [((t)
BuNC)(5)Cr=(CNPr2)-Pr-i]Br (7b), Similarly, 3b is converted with TIPF6
and (t)BuNC to [((t)BuNC)(3)(CO)(2)Cr=(CNPr2)-Pr-i]PF6 (6b), which re
acts with (t)BuNC in refluxing THF to give [((t)BuNC)(5)Cr=(CNPr2)-Pr-
i]PF6 (7b').