Seven-coordinated 2,2':6'2''-terpyridinemolybdenum(II) complexes: Synthesis, structure and reactivity of [Mo(CO)(C7H8)(4,4',4''-R(3)terpy) X]X' (R=H or (t)Bu)

The norbornadiene(terpyridine) complex [Mo(CO)(C7H8)(terpy)I]I (2a) is prepared in two steps from [Mo(CO)(4)(C7H8)] (1), iodine and 2,2':6',2 ''-terpyridine. On treatment with either KPF6 in methanol or AgSbF6 in CH2Cl2 the more soluble salts [Mo(Co)(C7H8)(terpy)I]PF6 (2b) and [Mo(CO)(C7H8)(terpy)I]SbF6 (2c) are isolated with good yields. With 4,4',4 ''-tri-tert-butyl-2,2':6',2 ''-terpyridine, in similar reactions the tert-butyl-substituted terpyridine compounds [Mo(CO)(C7H8)(4,4',4 ''-(t)Bu(3)terpy)I]X (X = I(3a), PF6(3b) or SbF6 (3c)) can be obtained, while the oxidation of 1 with two equivalents of CuBr2 leads to the bromo(terpyridine) complexes [Mo(CO)(C7H8)(terpy)Br]X (X = Br(4a), PF6 (4b) or SbF6 (4c)). The X-ray structural analysis for 4c reveals an unusual arrangement for the ligands around the metal center. A triangle formed by the norbornadiene and the halogen is perpendicular to the plane formed by terpyridine and CO. The iodo compound 2a as well as the bromo analogue 4a reacts with a double quantity of AgSbF6 by halogen abstraction to give a complex of the composition {[Mo(CO)(C7H8)(terpy)](2)(acetone)}(SbF6)(4) (5). Treatment of 5 with two equivalents of PMe(3) affords the phosphine complex [Mo(CO)(C7H8)(terpy)PMe(3)](SbF6)(2)-acetone (6). The similar compound [Mo(CO)(C7H8)(terpy)NCCH2CH3](SbF6)(2) (7), which can be easily prepared from 5 and a fivefold excess of propionitrile, exists in acetone in a concentration-dependent equilibrium with 5. In the presence of NaN3 or NaCl, 5 yields the complexes [Mo(CO)(C7H8)(terpy)X]SbF6 (X = N-3 (8) or Cl(9)). Whereas the azido compound 8 seems to be stable towards coordinating solvents, the chloro complex 9 slowly reacts in acetone.