CHELATE COMPLEXES WITH ALIPHATIC TRIPODAL TRIISOCYANIDE LIGANDS - SYNTHESIS AND CRYSTAL-STRUCTURES OF FAC-([HC(CH2CH2CH2NC)3]W(CO)3), FAC-([N(CH2CH2CH2NC)3]W(CO)3), AND THE DIMER FAC,FAC-([N(CH2CH2CH2NC)3]W(CO)3)2

The aliphatic tripodal triisocyanide ligands 3,3',3''-Nitrilotripropyl isocyanide (5) and 3,3',3''-Methylidynetripropyl isocyanide (9) react with (cycloheptatriene)metal carbonyls (M = Cr, W) to give the chelate complexes fac-{[HC(CH2CH2CH2NC)3]M(CO)3} [10; M = Cr (a), W (b)], and w-{[N(CH2CH2CH2NC)3]W(CO)3} (11). If the reaction of 5 with (C7H8)W(CO)3 is carried out at a high concentration of the reactants, the dimer fac,fac-{[N(CH2CH2CH2NC)3]W(CO)3}2 (12) can be isolated in a small (up to 5%) yield together with 11. 10b, 11, and 12 have been characterized by single-crystal X-ray structure analyses. Crystallographic data for 10b [11] {12} are as follows: formula C16H19N303W [C15H18N403W] {C30H36N8O6W2}, crystal system monoclinic [monoclinic] {monoclinic}, space group P2(1) [P2(1)] {P2(1)/c}, a = 7.974(2) [7.8685(12)] {8.557(3)} angstrom, b = 13.588(2) [13.468(3)] {11.269(6)} angstrom, c = 8.104(2) [8.1525(11)] {19.004(7)} angstrom, beta = 99.52(3) [98.501(12)] 199.51(3)}-degrees, and Z = 2 [2] {2} The monomeric complexes of 5 and 9 contain three 12-membered chelate rings, the smallest rings observed so far for facially coordinated tripodal triisocyanides. The central nitrogen atoms of the ligand 5 in the complexes 11 and 12 are not protonated and assume the ''in'' conformation. In 10b the central methine unit is also found in the in configuration, with the C-H vector pointing toward the tungsten atom. This behavior could be predicted from the signal for the methine proton in the H-1 NMR spectrum of 10. This signal is shifted downfield by approximately 1 ppm compared to the corresponding signal for the free ligand due to deshielding of the proton by the NC triple bonds, which is indicative of the in configuration.