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Neopentane‐Based Tripodal CpL 2 Ligands: Synthesis and Reactions of CH 3 C(CH 2 ‐η 5 ‐C 5 H 4 )(CH 2 ‐η 1 ‐PPh 2 ) 2 RuCl; Hindered Rotation of Vinylidene Ligands
Author(s) -
Urtel Katrin,
Frick Axel,
Huttner Gottfried,
Zsolnai Laszlo,
Kircher Peter,
Rutsch Peter,
Kaifer Elisabeth,
Jacobi Albrecht
Publication year - 2000
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/(sici)1099-0682(200001)2000:1<33::aid-ejic33>3.0.co;2-j
Subject(s) - chemistry , carbene , medicinal chemistry , ligand (biochemistry) , nitrile , deprotonation , stereochemistry , alkylation , derivative (finance) , organic chemistry , catalysis , ion , biochemistry , receptor , financial economics , economics
The tripodal ligand [CH 3 C(CH 2 C 5 H 4 )(CH 2 PPh 2 ) 2 ] – reacts with RuCl 2 (PPh 3 ) 3 to produce CH 3 C(CH 2 ‐η 5 ‐C 5 H 4 )(CH 2 ‐η 1 ‐PPh 2 ) 2 RuCl, [ tripod CpL 2 RuCl], 1 . Complex 1 undergoes substitution of the chlorine function with various nucleophiles L′ to produce [ tripod CpL 2 RuL′] + . The carbonyl derivative (L′ = CO) 2 , isonitrile (L′ = RNC) 3 , nitrile compounds (L′ = RCN) 4 , and a tolane adduct (L′ = η 2 ‐PhC≡CPh) 5 are obtained when 1 is treated with the appropriate ligands in polar solvents. Halide acceptors (e.g. TlPF 6 ) are generally needed to promote these reactions. The cyanide derivative tripod CpL 2 RuCN ( 3a ) is alkylated by F 3 CSO 3 CH 3 to give the isonitrile derivative [ tripod CpL 2 RuCNMe] + 3b . Terminal alkynes HC≡CR produce vinylidene compounds [ tripod CpL 2 RuL′] + , where L′ = CCHR (R = t Bu, 7b ; R = Ph, 7c ), or allenylidene derivatives, L′ = CCCPh 2 ( 6 ), depending on the nature of R (R = CPh 2 OH for synthesis of 6 ). Trimethylsilylacetylene gives the parent vinylidene species, L′ = CCH 2 ( 7a ), which is transformed to the Fischer‐type carbene compound, L′ = C(OMe)Me ( 8 ), upon treatment with methanol. The vinylidene species 7 are deprotonated by NaOMe to produce the alkynyl compounds tripod CpL 2 RuC≡CR ( 9 ). Methylation of 9 with F 3 CSO 3 CH 3 results in the vinylidene derivatives L′ = CC(Me)R (R = t Bu, 7d ; R = Ph, 7e ), having two organic substituents at the terminal carbon centre. For all vinylidene compounds with two different substituents at their terminal carbon atom, hindered rotation of the single‐faced vinylidene π‐ligand about its Ru–C bond is observed. Analysis by 31 P‐NMR spectroscopic coalescence measurements as well as line‐shape analyses reveals activation enthalpies of around 40 kJmol –1 for this rotation, with small activation entropies of around ±10 Jmol –1 K –1 . Solid‐state structures of nine compounds of the type [ tripod CpL 2 RuL′] + n ( n = 0, 1) demonstrate the remarkable conformational rigidity of the tripod CpL 2 Ru template. They also show that the possible strain imposed by linking the Cp ligand and the two donor groups L in one and the same chelate scaffolding does not appear to impose a serious steric strain on these templates.