Anorganische Chemie - Beckhaus

Cyclische isomere vier- und fünfgliedrige heterodinucleeare Fischer-Carbenkomplexe - gebildet aus einem Vinylidentitanocen-Fragment und Metallcarbonylen

R. Beckhaus , J. Oster, T. Wagner
Chem. Ber. 1994, 127, 1003 - 1013

The four-membered heterodimetallic carbene complexes Cp*

2

TiC(=CH

2

)C(=ML

n

)O 16 [L

n

M: Cr(CO)

5

(a), Mo(CO)

5

(b), W(CO)

5

(c), CpRe(CO)

2

(f), Mn

2

(CO)

9

(g), Re

2

(CO)

9

(h), Fe(CO)

4

(i), Rh(acac)(CO) (j)] are easily prepared by trapping the vinylidene titanocene [Cp*

2

Ti=C=CH

2

] fragment 6 with the corresponding metal carbonyls. The vinylidenetitanocene 6 is generated in a favourable manner from Cp*

2

Ti(CH

3

)CH=CH

2

(13) or Cp*(Fv)TiCH=CH

2

(14) [Fv: C

5

(CH

3

)

4

CH

2

] by a 1,3-H shift (a elimination) at room temperature. The formation of 16 is characterized by a preferred suprafacial [2+2] cycloaddition. Starting from Cp*

2

TiC(=CH

2

)CH

2

CH

2

(5) or 14 and transition metal carbonyls unexpected isomeric five-membered titanacycles Cp*

2

TiCH=CH-C(=ML

n

)O 8 [ML

n

= a-c, MnCp(CO)

2

(d), MnCp'(CO)

2

(e), f-i] are obtained at higher temperatures (70-100 °C). These oxatitanaclopentenes 8 are formed also upon heating via the kinetic product 16 with high yield, as a result of a 1,2-hydrogen shift, proved for c, g, h. From the spectroscopic data an e

1

-vinylcarbene structure is deduced, exhibiting a cis- (16) or trans-configurated (8) L

n

M=C-C=C sequence. An X-ray structure analysis shows the importance of the acyl resonance form in 8a, typically observed for such heterodimetallic carbene complexes. The reversible liberation of the metal carbonyl is a remarkable property of complexes 16 in solution, whereas the thermodynamic product 8 shows the typical properties of Fischer carbene complexes.