Vanadium, niobium, and tantalum hexacarbonylmetalate(-I) derivatives of several heterocyclic nitrogen bases, R,B[M(CO)& (R = H, Me; n = 1, Z), have been synthesized. In some cases an electron transfer from the hexacarbonylmetalate to the protonated or methylated BW+ cation has been observed. Pyridinium halides react with Na[M(CO)6] (M = Nb, Ta) in the presence of 1 equiv of 1,2-bl(diphenylphosphino)ethane (diphos) to give high yields of the halo tetracarbonyl derivatives MX(CO)4(diphos). The red-orange TaI(CO)4(diphosc)o mplex has been studied by X-ray diffraction methods. Crystal data: space group P2,/n; M, 818.3; a = 14.864 (10) A, b = 9.875 (7) A, c = 19.335 (13) A; p = 105.61 ( 2 ) O ; U = 2733 (3) A3; 2 = 4; Ddd = 1.988 g ~ m -F~(O;O 0) = 1568; ~ ( MKoa ).= 52.4 cm-'. The geometry of the seven-coordinatet antalum atom is best described as a capped trigonal prism with the iodide ligand in the capping position. By reaction of Na[Ta(CO)6] with 1 equiv of hydrogen chloride and diphos in toluene, the hydride TaH(CO),(diphos) has been isolated in good yield.