Komplexchemie at P-reicher Phosphane und Silylphosphane. VI. Bildung und Struktur der Chromcarbonylkomplexe des Tris(trimethylsilyl) heptaphosphanortricyclans (Me3Si)3P7

Formation and Structures of Chromium Carbonyl Complexes of Tris(trimethylsily)heptanortricyclane (Me₃Si)₃P₇ (Me₃Si)₃P₇ 1 reacts with one equivalent of Cr(Co)₅THF 2 to give the yellow (Me₃Si)₃P₇Cr(Co)₅] 4. The Cr(Co)₅group is attached to a P^e atom. Yellow (Me₃Si)₃P₇Cr(CO)₅]₂ 5 is obtained either from reacting 1 with two equivalents of 2 , or from 4 with one equivalent of 2. One Cr(CO)₅ groups in 5 is coordinated to a P^e atom, the other one to a P,^b atom. Similarly, Yellow (Me₃Si)₃P₇Cr(CO)₅]₃ 6 results from reacting 5 with one equivalent of 2 . Two Cr(CO)₅ groups in 6 are linked to P^b atoms, and the third one either to a P^e or the P^a atom (assignment not completely clear). Derivatives containing a P^e bridge appear in reactions of 1 with higher amounts of 2 . Such, 5 forms mixtures of the red compounds (Me₃Si)₃P₇ × Cr(CO)₅]₂Cr(CO)₄] 8 and (Me₃Si)₃P₇Cr(CO)₅] × Cr(CO)₄] 9 , and even preferably 9 with four equivalents of 2 . In 8 , one Cr(CO)₅ group is attached to that p^e atom which is not engaged in the Cr(CO)₄ bridge, and the second to one of the P^b atoms directly adjacent to the bridge. The additional Cr(CO)₅ group in 9 is coordinated to the remaining P^b atom directly adjacent to the bridge. In reactions of 5 with even higher amounts of 2 , four Cr(CO)₅ groups and one Cr(CO)₄ bridge attach to the basic P₇ skeleton to from the less stable Me₃P₇Cr(CO)₅]₄Cr(CO)₄]. (Me₃Si)₃P₇ 1 reacts considerably slower with Cr(CO)₅THF 2 than R₃P₇ (R = Et, iPr). Cr(CO)₄NBD 3 reacts with 1 , but it was not possible to isolate (Me₃Si)₃P₇Cr(CO)₄]. However, 4 with 3 forms (Me₃Si)₃P₇Cr(CO)₅]Cr(CO)₄] 7 , and 5 with 3 yields (Me₃Si)₃P₇Cr(CO)₅]₂Cr(CO)₄] 8 . The structures of 4 , 5 , 7 , 8 or 9 are quite analogous to those of the derivatives of Et₃P₇ but there exist significant differences in stability and reactivity. While Et₃P₇Cr(CO)₅]₂ in solution rearranges to give the stable Et₃P₇Cr(CO)₅]Cr(CO)₄], the analogous (Me₃Si)₃P₇Cr(CO)₅]Cr(CO)₄] 7 is not stable and is not obtained from (Me₃Si)₃P₇Cr(CO)₅]₂ 5 . Et₃P₇Cr(CO)5]₃ can just be detected spectroscopically and rearranges easily to give Et₃P₇Cr(CO)₅]₂ Cr(CO)₄] whereas (Me₃Si)₃P₇Cr(CO)₅]₃ 6 can be isolated. These differences are caused by the greater steric requirements of Me₃Si groups. The formation of a P^e–Cr(CO)₄–P^e bridge, e.g., requires a Me₃Si group in 1 to switch from the s to the as position. Whereas many of the complex compounds of R₃P₇ (R = Et, iPr) crystallize easily, the analogous derivatives of (Me₃Si)₃P₇ did not yield crystals. The structures of the products were assigned by evaluating the coordination shift in their ₃₁P NMR spectra and by comparision of these spectra with those of such derivatives of Et₃P₇ which previously had been investigated by single crystal structure determinations.