Stabilisierung niedervalenter Ni(CO)-Bausteine durch [Ti](CCR)2; Reaktionsverhalten von {[Ti](CCR)2}Ni(CO) gegenüber Triphenylphosphan und Phosphiten

The preparation of heterobimetallic transition metal complexes of the type {[Ti](CCR)2}Ni(CO) {R=SiMe3: 3a, [Ti]=(η5-C5H5)2Ti; 3b: [Ti]=(η5-C5H5)(η5-C5H4SiMe3)Ti; 3c, [Ti]=(η5-C5H4SiMe3)2Ti; R=tBu: 3d, [Ti]=(η5-C5H4SiMe3)2Ti; R=Ph: 3e, [Ti]=(η5-C5H4SiMe3)2Ti}, in which next to an early (Ti) a late (Ni) transition metal is present, is described. Additionally, the reaction chemistry of 3a and 3c towards P(OR′)3 (4a, R′=CH3; 4b, R′=C6H5; 4c, R′=C6H4Me-2; 4d, R′=C6H4tBu-2) is reported. In these reactions the nickel-bound carbonyl ligand is replaced by P(OR′)3 producing {[Ti](CCSiMe3)2}Ni[P(OR′)3] {[Ti]=(η5-C5H5)2Ti: 5a, R′=CH3; 5b, R′=C6H5; 5c, R′=C6H4Me-2; [Ti]=(η5-C5H4SiMe3)2Ti: 5d, R′=CH3; 5e, R′=C6H5} along with Ni(CO)2[P(OR′)3]2 (6a, R′=C6H5; 6b, R′=C6H4Me-2; 6c, R′=C6H4tBu-2). It appeared that the latter reaction strongly depends on the sterical demand, Tolman cone angle, of the respective phosphites used: while, in the reaction of 3a or 3c with 4a selectively 5a and 5d is formed, with more bulky substituents R′, e.g. R′=C6H5 and C6H4Me-2, complexes 5b and 5c along with 6a and 6b are produced. Changing to even more sterical demanding groups such as R′=C6H4tBu-2 than exclusively 6c is formed. The dynamic behaviour of 5 in solution is discussed. When 3a is treated with equimolar amounts of PPh3 (7) the titanium–nickel alkynyl species [Ti](μ-η1:η2-CCSiMe3)Ni(PPh3)(μ-η1:η2-CCSiMe3) {8a, [Ti]=(η5-C5H5)2Ti} is accessible via an alkynyl-transfer reaction from titanium to nickel. However, on treatment of 3c with 7 no reaction occurs. Arguments for the different behaviour of 3a–3c towards 4 and 7 will be presented. The result of the X-ray structure analysis of complexes 5d and 5e are reported. Both complex crystallize in the monoclinic space group P21/n. Cell parameters for 5d: a=10.9390(10), b=15.585(4), c=22.950(3) Å, β=92.861(7)°, V=3907.7(14) Å3, Z=4 and δ=1.189 g mol−1. 5e: a=17.694(9), b=22.620(10), c=24.510(10) Å, β=103.90(4)°, V=9523(8) Å3, Z=8 and δ=1.236 g mol−1. In both complexes a low-valent Ni[P(OR′)3] building block (5d, R′=CH3; 5e, R′=C6H5) is stabilised by the chelating effect of the organometallic π-tweezer [Ti](CCSiMe3)2, giving rise to a trigonal-planar environment at the nickel atom. The early (Ti) and late (Ni) transition metal centers are thereby bridged via the σ- and π-bound alkynyl groups Me3SiCC. The influence of the different sterical demanding phosphites onto the [Ti](CCSiMe3)2 framework will be discussed.