Synthesis, Characterization and Stability of Spirodiene Complexes of Molybdenum(II): New Route to ansa ‐Molybdenocene and Ring‐Functionalized Molybdenocene Compounds

The reactions of [Mo(CO) 2 (Cp)(NCCH 3 ) 2 ][BF 4 ] ( 1 ) with spiro[2.4]hepta‐4,6‐diene and spiro[4.4]nona‐1,3‐diene give the complexes [Mo{η 4 ‐C 5 H 4 (CH 2 ) 2 }(CO) 2 (Cp)][BF 4 ] ( 3 ) and [Mo{η 4 ‐C 5 H 4 (CH 2 ) 4 }(CO) 2 (Cp)][BF 4 ] ( 4 ), respectively. [Mo{η 4 ‐C 5 H 4 (CH 2 ) 2 }(CO) 2 (Cp)][BF 4 ] ( 3 ) is stable towards ring opening at room temperature, but its formation is accompanied by small amounts of ring‐opening products [Mo(η 5 ‐C 5 H 4 CH 2 ‐η 1 ‐CH 2 )(CO)(Cp)][BF 4 ] ( 5 ) and [Mo{η 5 ‐C 5 H 4 (CH 2 ) 2 ‐η 1 ‐CO}(CO)(Cp)][BF 4 ] ( 6 ). With 1,1‐dimethyl‐spiro[2.4]hepta‐4,6‐diene, two isomers with the formula [Mo{η 4 ‐C 5 H 4 CH 2 C(CH 3 ) 2 }(CO) 2 (Cp)][BF 4 ] are formed ( 7 and 8 ). While the endo ‐isomer 7 is stable towards ring opening, the exo ‐isomer 8 slowly rearranges to the ring‐opened product [Mo{η 5 ‐C 5 H 4 C(CH 3 ) 2 CH 2 ‐η 1 ‐CO}(CO)(Cp)][BF 4 ] ( 9 ). The reaction of [Mo(CO) 2 (Ind)(NCCH 3 ) 2 ][BF 4 ] ( 2 ) with spiro[4.4]nona‐1,3‐diene also gives the diene coordinated species [Mo{η 4 ‐C 5 H 4 (CH 2 ) 4 }(CO) 2 (Ind)][BF 4 ] ( 11 ), which is the first example of a structurally characterized, coordinated, unsubstituted spirodiene. In contrast, reaction of 2 with spiro[2.4]hepta‐4,6‐diene leads directly to the ansa ‐cyclopentadienyl complex [Mo(η 5 ‐C 5 H 4 CH 2 ‐η 1 ‐CH 2 )(CO)(Ind)][BF 4 ] ( 12 ). Reaction of 12 with bromine or iodine leads to the formation of Cp‐substituted molybdenocene derivatives [Mo{η 5 ‐C 5 H 4 (CH 2 ) 2 X}(CO)(Ind)X][BF 4 ] ( 13 : X = Br, 14 : X = I). The compounds [Mo(η 5 ‐C 5 H 4 CH 2 ‐η 1 ‐CH 2 )(CO)(Ind)][BF 4 ] ( 12 ) and [MoBr{η 5 ‐C 5 H 4 (CH 2 ) 2 Br}(CO)(Ind)][Br] · 0.5H 2 O ( 13a ) were structurally characterized, and they open the way to new functionalized molybdenocene complexes that have biological applications.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)