ALLYL CARBORANE COMPLEXES OF MOLYBDENUM AND TUNGSTEN - CAGE HYDRIDE ABSTRACTION REACTIONS IN THE PRESENCE OF DONOR MOLECULES

Treatment of the sets [NEt4] o(CO)2(eta3-C3H5)(eta5-7,8,-R'2-7,8-C2B9H 9)]dagger (R' = H (1a) or Me (1b)) in CH2Cl2 With [CPh3][BF4] in the p resence of donor molecules L affords the complexes [Mo(CO)2(eta3-C3H5) (eta5-7,8-R'2-7,8-C2B9H8-10-L)] (R' = H, L = OEt2 (2a); R' = Me, L = O Et2 (2b), thf (tetrahydrofuran) (2d), SMe2 (2e), PPh3 (2f), NCsH5 (2g) , or 4,4'-NC5H4C5H4N (2h)). The tungsten compound (CO)2(eta3-C3H5)(eta 5-7,8-Me2-7,8-C2B9H8-10-OEt2)] (2c) has been similarly prepared from [ NEt4][W(CO)2(eta3-C3H5)(175-7,8-Me2-7,8-C2B9H9)] (1c). The structure o f 2b has been established by X-ray crystallography. Crystals are tricl inic, space group P1BAR (No. 2) with a = 7.106(1) angstrom, b = 9.088( 2) angstrom, c = 16.271(2) angstrom, a = 75.08(1)-degrees, beta = 92.7 7(1)-degrees, gamma = 102.19(1)-degrees, and Z = 2. The molybdenum ato m is ligated on one side by two essentially linearly bound CO molecule s and the allyl group, the latter adopting an eta3-bonding mode (Mo-C = 2.342(4), 2.234(4), and 2.365(4) angstrom). On the other side, the m olybdenum atom is coordinated by the open pentagonal face of the nido- 7,8-C2B9 fragment. The boron atom in this face which is in the beta-si te with respect to the two carbons carries an OEt2 molecule as an exop olyhedral substituent (B-0 = 1.544(3) angstrom). Thus, 2b is a zwitter ionic complex with formally a plus charge on the oxygen atom and a neg ative charge on the molybdenum atom. Treatment of CH2Cl2 solutions of 2b and 2c, respectively, with K[BH{CH(Me)(Et)}3], followed by addition of [NEt4]-Cl, affords the species [NEt4] M(CO)2(eta3-C3H5)(eta5-7,8-M e2-7,8-C2B9H8-10-OEt)] (M = Mo (3a) and W (3b)). Similarly, treatment of tetrahydrofuran solutions of 2b-2d with [NEt4]F gives the salts 3a, 3b, and [NEt4] a3-C3Hr5){eta5-7,8-Me2-7,8-C2B9H8-10-0(CH2)3CH2F}] (3c ), respectively. Protonation (HBF4.Et2O) of the species 3, in CO-satur ated CH2CI2 solutions, yields the complexes [M(CO)4(eta5-7,8-Me2-7,8-C 2B9H8-10-OEt)] (M = Mo (4a), W (4c)) and [Mo(CO)4{eta5-7,8-Me2-7,8-C2B 9H8-10-0(CH2)3CH2F}] (4d), respectively. In CH2Cl2 solutions at room t emperature, compound 4a slowly converts to its polytopal isomer [Mo(CO )4(eta5-2,8-Me2-2,8-C2B9H8-10-OEt)](4b). Complexes 4a and 4b react wit h [W(=CC6H4Me-4)(CO)2(eta5-C5H5)] in CH2CI2 to give, respectively, the isomeric dimetal compounds (CO)3-(eta5-C5H5)(eta5-n,8-Me2-n,8-C2B9H8- 10-OEt)] (n = 7, 6a; n = 2, 6b). The structure of 6b has been establis hed by X-ray crystallography. Crystals are monoclinic, space group C2/ c (No. 15) with a = 28.763(3) angstrom, b = 10.950(3) angstrom, c = 18 .030(1) angstrom, beta = 94.785(7)-degrees, and Z = 8. The Mo-W bond ( 2.645(1) angstrom) is spanned by the p-tolylmethylidyne group (mu-C-Mo = 2.088(7) angstrom, mu-C-W = 1.961(7) angstrom). The tungsten atom a s expected carries the C5H5 ring and a CO molecule, while the molybden um atom is coordinated by two CO groups and is also bonded to the five atoms in the open CBBBB face of the carborane cage, forming with the latter an icosahedral 2,1,8-MoC2B9 framework. A boron atom beta to the carbon in the CBBBB ring ligating the molybdenum carries the OEt subs tituent (B-0 = 1.41 (1) angstrom), and the BH vertex between the BOEt and CMe vertices forms an exopolyhedral B-H half arrow pointing right W linkage (B-W = 2.415(9) angstrom, mu-H-B = 1.11 angstrom, mu-H-W = 1 .87 A). The new complexes have been characterized by IR and NMR spectr oscopy, in addition to the X-ray diffraction studies.