FROM END-ON COORDINATION OF ACETONITRILE MOLECULES TO CROSSWISE BRIDGING - FORMATION OF IMINOPHOSPHINO AND ACETAMIDATE LIGANDS IN A DIMOLYBDENUM COMPLEX BY FURTHER REACTIONS WITH NUCLEOPHILES

Three complexes from the reaction of bis(diphenylphosphino)ethane (dpp e), water and acetonitrile have been structurally characterized. React ion of the quadruply M-M bonded complex [Mo-2(CH3CN)(8) (ax-CH3CN)][BF 4](4) (1a), with dppe produces [Mo-2(mu,eta(2)-CH3CN) (mu,eta(1)-NC(CH 3)P(Ph-2) CH2CH2PPh2) (CH3CN)(7)][BF4](4) (2), in which an acetonitril e molecule is bound to both Mo atoms in a perpendicular mode. A new ch elating ligand, namely NC(CH3)P(Ph-2) CH2CH2PPh2, is formed by couplin g of a dppe to an acetonitrile molecule. It bridges both Mo atoms with its N atom and chelates to one of the Mo atoms with both N and P atom s. When a trace amount of water is introduced into 2 at low temperatur e, the compound [Mo-2(mu,eta(2)-CH3CNBF3) (mu,eta(1)-N(H)COCH3) (CH3CN )(8)][BF4](3) (3), is obtained. It has a crosswise bridging acetonitri le moiety; the nitrogen atom of this bridging acetonitrile is also coo rdinated to a BF, group in the solid state. An acetamidate ligand, ins tead of the coupled dppe group, bonds to both Mo atoms symmetrically u sing only the N atom. Hydrogen bonding is observed between the amide N H group and one F atom of one of the BF; counteranions. Both compounds 2 and 3 have edge-sharing bioctahedra and elongated Mo-Mo distances. By adding an excess of water to the solution of 2, complex [Mo-2(mu-N( H) COCH3)(2)(CH2CN)(4)] [BF4](2) (4) is produced. The crystal structur e of 4 shows two cis bridging acetamidate ligands. The N and O atoms o f each acetamido group coordinate to the Mo atoms and they are evenly distributed on two positions. The results are rationalized as nucleoph ilic attacks of dppe or water molecules on coordinated acetonitrile li gands on the dimolybdenum complexes. (C) 1998 Elsevier Science Ltd. Al l rights reserved.