Seven-coordinated 2,2′ : 6′2″-terpyridinemolybdenum(II) complexes: synthesis, structure and reactivity of [Mo(CO) (C 7H 8) (4,4′,4″-R 3 terpy) X]X′ ( [formula omitted

Abstract

The norbornadiene(terpyridine) complex [Mo(CO)(C 7H 8)(terpy)I]I ( 2a) is prepared in two steps from [Mo(CO) 4(C 7H 8)] ( 1), iodine and 2,2′ : 6′,2″-terpyridine. On treatment with either KPF 6 in methanol or AgSbF 6 in CH 2Cl 2 the more soluble salts [Mo(CO)(C 7H 8)(terpy)I]PF 6 ( 2b) and [Mo(CO)(C 7H 8)(terpy)I]SbF 6 ( 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)(C 7H 8)(4,4′,4″- tBu 3terpy)I]X ( X = I( 3 b , PF 6( 3b) or SbF 6 ( 3c)) can be obtained, while the oxidation of 1 with two equivalents of CuBr 2 leads to the bromo(terpyridine) complexes [Mo(CO)(C 7H 8)(terpy)Br]X ( X = Br( 4 a ) , PF 6 ( 4b) or SbF 6 ( 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 AgSbF 6 by halogen abstraction to give a complex of the composition {[Mo(CO)(C 7H 8)(terpy)] 2(acetone)}(SbF 6) 4 ( 5). Treatment of 5 with two equivalents of PMe 3 affords the phosphine complex [Mo(CO)(C 7H 8)(terpy)PMe 3](SbF 6) 2-acetone ( 6). The similar compound [Mo(CO)(C 7H 8)(terpy)NCCH 2CH 3](SbF 6) 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 NaN 3 or NaCl, 5 yields the complexes [Mo(CO)(C 7H 8)(terpy)X]SbF 6 (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.