Unprecedented eta1-P basal Coordination of P4X3 Molecules (X = S, Se). An Experimental and Theoretical Study of the Apical vs. Basal Complexation Dichotomy

Reaction of [(triphos)Re(CO)2(OTf)] (1) [triphos ) MeC(CH2PPh2)3; OTf ) OSO2CF3] with P4S3 and P4Se3 yields pairs of coordination isomers, namely, [(triphos)Re(CO)2{è1-Papical-P4X3}]+ (X ) S, 2; Se, 5) and [(triphos)Re- (CO)2{è1-Pbasal-P4X3}]+ (X ) S, 3; Se, 6). The latter represent the first examples of the è1-Pbasal coordination achieved by the P4X3 molecular cage. Further reaction of 2/3 and 5/6 mixtures with 1 affords the dinuclear species [{(triphos)Re(CO)2}2{í,è1:1-Papical,Pbasal-P4X3}]2+ (X ) S, 4; Se, 7) in which the unprecedented M-è1-Pbasal/è1- Papical-M¢ bridging coordination of the P4X3 molecule is accomplished. A theoretical analysis of the bonding properties of the two coordination isomers is also presented. The directionality of apical vs basal phosphorus lone pairs is also discussed in terms of MO arguments.