Syntheses and properties of organocyanamide, cyanoguanidine and dinitrogen complexes of rhenium. Crystal structure of mer-[ReCl2(NCNEt2)(PMePh2)3]

Treatment of a THF solution of trans-[ReCl(N2)L4] (L = PMePh2) with a cyanamide, NCNR2 (R = Me, Et or H) or with cyanoguanidine, NCNC(NH2)2 , yields mer-[ReCl(N2)(NCNR2)L3] (1) or mer-[Re(N2)[Re(N2){NCNC(NH2)2}2L3]Cl (2), respectively, which, to our knowledge, are the first mixed dinitrogen-cyanamide-type complexes to be reported. The former products (1, R = Me or Et) can also be obtained from reaction of the benzoyldiazenido complex [ReCl2(NNCOPh)L3] with NCNR2 in refluxing methanol; the Re(II) complex mer-[ReCl2(NCNEt2)L3] (3) is also formed (conceivably via an unusual homolysis of the CN bond of the benzoyldiazenido ligand) and its crystal structure is reported. It shows an unusual pyramidal conformation at the amine N atom of the diethylcyanamide ligand which also exhibits a significant structural trans influence on the phosphine, behaving as a stronger net electron donor than the latter ligand.