COORDINATIVELY UNSATURATED DERIVATIVES OF GROUP-6 METAL-CARBONYLS CONTAINING THE PI-DONATING LIGAND 3,5-DI-TERT-BUTYLCATECHOLATE

The series of group 6 metal tricarbonyl derivatives of di-tert-butylca techolate have been synthesized from the reactions of M(CO)(5)THF (M = Cr, Mo, W) with 2 equiv of [Et(4)N][3,5-(t)Bu(2)OC(6)H(2)OH]. Subsequ ent removal of the free catechol was achieved by the addition of NaOMe . The complexes were shown by X-ray crystallography to exhibit coordin atively unsaturated M degrees centers. These metal dianions which have formally 16e(-) configurations are stabilized by pi-donation from the oxygen atoms of the catecholate ligand. This is evident from the shor t M-O bond distances, e.g., for M = W, 2.059(6) Angstrom vs 2.151(4) A ngstrom for a single bond. The structures of these five-coordinate dia nions can be loosely defined as trigonal bipyramidal with the more ele ctron-rich oxygen donor of the catecholate (ortho to the electron-rele asing tert-butyl substituent) occupying an equatorial site as indicate d by a shorter M-O bond length. The tungsten derivative was shown to r eversibly react with CO or phosphines to afford the 18e(-), saturated complexes. Although the molybdenum tricarbonyl derivative reacts with CO to partially provide the tetracarbonyl complex, the analogous proce ss involving chromium did not occur. That is, the formation of an O--> M pi bond vs an additional M-CO bond is favored for M = chromium. Comp lex 2, [Et(4)N](2)[W(CO)(4)DTBCat], crystallizes in the monoclinic spa ce group P2(1)/c with a = 10.013(5) Angstrom, b = 43.921(14) Angstrom, c = 9.113(4) Angstrom, beta = 115.76(3)degrees, V = 3609(3) Angstrom( 3), and d(calc) = 1.429 g/cm(3), for Z = 4. Complex 4, [Et(4)N](2)[Mo( CO)(3)DTBCat], crystallized in the monoclinic space group C2 with a = 18.255(7) Angstrom, b = 8.596(3) Angstrom, c = 22.369(7) Angstrom, bet a = 91.05(6)degrees, V = 3510(2) Angstrom(3), and d(calc) = 1.251 g/cm (3), for Z = 4. Similarly, complex 5, [Et(4)N](2)[Cr(CO)(3)DTBCat], cr ystallized in the monoclinic space group C2 with a = 18.09(2) Angstrom , b = 8.553(3) Angstrom, c = 21.927(11) Angstrom, beta = 91.09(8)degre es, V = 3393(4) Angstrom(3), and d(calc) = 1.208 g/cm(3), for Z = 4.