Crystal and molecular structure of a new eight-membered tetraphospha-macrocycle, (–PCPhCMeCMeC–)4

Abstract

A new P₄C₄ eight-membered macrocycle has been obtained in one step from 3,4-dimethyl-1-phenylphosphole. A comparison of the X-ray crystal structure of this P₄C₄ macrocycle with that of its decacarbonyldimolybdenum complex shows that the P₄C₄ crown gains a very high flexibility through an easy rotation of the adjacent phospholyl units round the C–C and P–P bonds of the central eight-membered ring. This means that this P₄C₄ macrocycle can adapt its shape to the stereochemical requirements of the complexed metals. The P–P and C–C bonds of the crown [average 2.191(3) and 1.47(1)Å respectively] are significantly shorter than normal P–P and C–C single bonds. Thus some conjugative interactions probably exist between the adjacent phospholyl rings. These interactions are suppressed in the decacarbonyldimolybdenum complex.