WHEN DOES A NITROGEN ATTACHED TO A LAMBDA-3-PHOSPHORUS ASSUME A PYRAMIDAL GEOMETRY - CRYSTAL-STRUCTURES OF GROUP-6 METAL-CARBONYL-COMPLEXESOF ISOMERIC FORMS OF LAMBDA-3-CYCLOTRIPHOSPHAZANES

The reaction of [Mo(CO)4(nbd)] (nbd = norbornadiene) with trans-[EtNP( OC6H3Me2-2,6)]3 (L1) or cis-[EtNP(OCH2CF3)]3 (L2) yields the mono- and di-nuclear molybdenum(o) complexes [Mo(CO)4(L1)] 1 and [{Mo(CO)4(mu-L 2)}2] 2, respectively. They represent the first organometallic transit ion-metal derivatives of lambda3-cyclotriphosphazanes and have been ch aracterised by elemental analysis and IR and NMR spectroscopy and thei r structures confirmed by X-ray crystallography. The different co-ordi nation behaviour of the cis and trans isomeric forms of this type of l igand is revealed. A pyramidal geometry observed around one of the nit rogen atoms of the P3N3 ring in complex 1 is unprecedented among lambd a3-phosphazanes.