The reaction of [{Cr(cp)(CO), },] (1) with 2 mol equivalents of P, in toluene at 90 "C produces a [Cr,(cp),(q5-P,)](5), the relative proportion of which is dependent on the duration of the reaction. This, coupled with thermolysis studies on (2)-( 4), demonstrates that these three complexes are the primary products of the reaction, whereas (5) arises mainly from the thermolysis of (2), which also yields (3) and [{Cr(cp)(CO),},] (6). Complex (5) has been isolated from a reaction of (1) with P, at 11 0 "C after ca. 5 h. A single-crystal X-ray diffraction study of ( 5) shows it to be a triple-decker sandwich complex with a cyclic P, ring bonded to t w o Cr(cp) groups. Crystal data: monoclinic, space group P2,/n, a = 7.921 (2), b = 15.04(1), c = 11.704(4) A, p = 104.08(2)", and Z = 4. The spectral features of complex (5) are also presented. mixture of [Cr2(cp),(Co),(~-rl2-P2)1 (21, [WCP) (CO),(rl3-PJl (3), [WCP) (co)2h(pd (4), and There is much current interest in the syntheses and reactivity of transition-metal complexes containing bare P atoms or aggregate^.'-^ In extending our studies on the reactions of the Cr-Cr dimer [(Cr(cp)(CO),),] (1) (cp = q5-C5H5) with main group elements,,g5 we have treated it with elemental phosphorus under mild reaction conditions and obtained high P3)] (3).6 In this paper, we describe conditions that led to the isolation of [Cr,(cp),(P,)] (5), together with evidence indicating that (5) arises from the thermolytic degradation of (2), (3), and a polyphosphidochromium complex [ { Cr(cp)-(CO)2}5(Plo)] (4). Mechanistic pathways for the formation of (3) and (5) and the X-ray crystal structure of (5) are also presented. yields of C C r 2 ( c ~) 2 ( C 0 ) 4 ( ~-~ 2-p2>1 (2) and [Cr(cp)(CO),(rl ,-
