Synthesis and Structure of the First η 3 ‐1,2‐Diphosphaallyl Complexes [(η 5 ‐C 5 H 5 )(CO) 2 M{η 3 ‐RPPC(SiMe 3 ) 2 }] (M = Mo, R = t Bu, Cy; M = W, R = t Bu) from [(η 5 ‐C 5 H 5 )(CO) 2 M=P=C(SiMe 3 ) 2 ] (M = Mo, W) and Inversely Polarized Phosphaalkenes RP=C(NMe 2 ) 2 (R = t Bu, Cy)

Reaction of [(η 5 ‐C 5 H 5 )(CO) 2 M=P=C(SiMe 3 ) 2 ] [where M = Mo ( 2 ), W ( 5 )] with the phosphaalkene t BuP=C(NMe 2 ) 2 ( 1a ) afforded the η 3 ‐1,2‐diphosphaallyl complexes [(η 5 ‐C 5 H 5 )(CO) 2 M{η 3 ‐ t BuPPC(SiMe 3 ) 2 }], [where M = Mo ( 3a ); M = W ( 6 )]. Similarly, 2 and CyP=C(NMe 2 ) 2 ( 1b ; where Cy = cyclohexyl) gave rise to the formation of [(η 5 ‐C 5 H 5 )(CO) 2 Mo{CyPPC(SiMe 3 ) 2 }] ( 3b ) by a phosphinidene transfer process. Small amounts of [{η 5 ‐C 5 H 5 )(CO) 2 Mo} 2 {η 2 :η 2 ‐Cy 3 P 5 }] ( 4 ) were formed as a minor product. However, treatment of 2 and 5 with HP=C(NMe 2 ) 2 ( 1c ) yielded the complexes [(η 5 ‐C 5 H 5 )(CO) 2 M{η 2 ‐(Me 3 Si) 2 CH–P=P–C(NMe 2 ) 2 }] [where M = Mo ( 9 ), W ( 10 )]. The novel compounds 3a , 3b , 9 and 10 were characterized by means of spectroscopy (IR, 1 H, 13 C{ 1 H}, 31 P{ 1 H} NMR, MS). Moreover, the molecular structures of 3a , 3b , 4 , 6 and 10 were determined by X‐ray diffraction analysis. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)