Da. Brown et al., SUBSTITUTION AND ADDITION-REACTIONS OF THE (CO)3(ETA-7-TROPYLIUM)M CATIONS (M=CR, MO, W) WITH TERTIARY DISPHOSPHINES, Organometallics, 13(7), 1994, pp. 2662-2667
The reactions of the title compounds I-III, [(eta7-C7H7)M(CO)3]BF4 (M
= Cr, Mo, and W, respectively), with the diphosphines PPh2(CH2)nPPh2 (
n = 1-4) at low temperatures (-40 to -60-degrees-C) form two new serie
s of complexes which are quite different from previous carbonyl substi
tution products. The first series (IV-VI) formed by the diphosphines (
n = 1-3) comprise 7-exo ring adducts involving the bonding of only one
phosphorus atom of the diphosphine to ring carbon atom 7 of I. The se
cond series (VII and VIII) are diphosphine ring linked dimers, e.g. [(
7,7'-exo-dppb){eta6-C7H7)Cr(CO)3}2][BF4]2, for which X-ray crystallogr
aphy confirms a diphosphine linked ring-ring structure with the Cr(CO)
3 moieties situated on opposite sides of the ring systems. The ring C-
phosphorus bond length of 1.852 angstrom indicates a relatively weak b
ond, consistent with facile cleavage of these adducts on reaction with
nucleophiles such as hydride.