A new class of remote N-heterocyclic carbenes with exceptionally strong σ-donor properties: introducing benzo[c]quinolin-6-ylidene.
We make the case for benzo[c]quinolin-6-ylidene (1) as a strongly electron-donating carbene ligand. The facile synthesis of 6-trifluoromethanesulfonylbenzo[c]quinolizinium trifluoromethanesulfonate (2) gives straightforward access to a useful precursor for oxidative addition to low-valent metals, to yield the desired carbene complexes. This concept has been achieved in the case of [Mn(benzo[c]quinolin-6-ylidene)(CO)5](+) (15) and [Pd(benzo[c]quinolin-6-ylidene)(PPh3)2(L)](2+) L = THF (21), OTf (22) or pyridine (23). Attempts to coordinate to nickel result in coupling products from two carbene precursor fragments. The CO IR-stretching-frequency data for the manganese compound suggests benzo[c]quinolin-6-ylidene is at least as strong a donor as any heteroatom-stabilised carbene ligand reported.
School of Chemistry, University of Bristol, Cantock's Close, Bristol, BS8 1TS, UK.
Ulrich F J
UF
Mayer
Elliot
E
Murphy
Mairi F
MF
Haddow
Michael
M
Green
Roger W
RW
Alder
Duncan F
DF
Wass