COORDINATION CHARACTERISTICS OF 3 N,N'-DI(AZOL-1-YL)METHANES - SUBSTITUENT EFFECTS ON INFRARED-ABSORPTION AND STRUCTURE OF THE GROUP-VI METAL-CARBONYL DERIVATIVES

Compounds [M(H2Caz2)(CO)4] (M = Cr, Mo, or W), were obtained readily a nd similarly by refluxing the equivalent amounts of N,N'-di(azol-1-yl) methanes, H2CAz2 (Az = pyrazol-1-yl (Pz), 3,5-dimethylpyrazol-1-yl (Pz ') or 3,4,5-trimethylpyrazol-1-yl (Pz'') with [M(CO),] (M - Cr, Mo, or W) in a mixed solvent system of 1,2-dimethoxyethane and tetrahydrofur an. Under phase transfer catalysis conditions this gives rise to the n ew nitrogen-bidentate ligand, H2CPz2'', by reaction of HPz'' with meth ylene chloride. IR absorption bands in the carbonyl region indicate th at no regular trends can be found for different substituents on the py razolyl ring. This irregularity is attributed to flexibility of the bo at conformation formed from the metal centre and the ligand, which is supported by comparative structure details of [Mo(H2CPz2')(CO)4], repo rted previously, [W(H2CPz2'')(CO)4] (6) and [W(H2CPz2')(CO)4] (7): 6, triclinic, P1BAR, a = 8.403(3), b = 9.589(3), c = 13.310(3) angstrom, alpha = 94.476(22), beta = 102.837(21), gamma = 110.355(25)-degrees, Z = 2, R = 0.024, R(w) = 0.023, based on 3070 with 1 > 2sigma (I). 7, m onoclinic, P2(1)/c, a = 9.178(3), b = 15.885(9), c = 12.394(10) angstr om, beta = 108.64(9)-degrees, Z = 4, R = 0.030, R(w) = 0,030, based on 2625 reflections with I > 2.5sigma(I).