Ruthenium phosphine pincer complex

Dehydrogenation of alcohols to aldehyde or ketone allows subsequent bond construction steps which would not be possible for the parent alcohols. Hence, a variety of iridium, rhodium or ruthenium phosphine, pincer and related complexes, that are efficient catalysts for the dehydrogenation of alcohols, can potentially be appHed for the related hydrogen-transfer reactions, thus leading to new added-value compounds. The hydrogen atoms transfer to a sacrificial hydrogen acceptor, such as a carbonyl compound or an olefin which is reduced to the corresponding alcohol or alkane. 

For example, the pyridine-based pincer complexes 1, 4, 7, and 10 undergo smooth deprotonation to provide complexes 2, 5, 8, and 11 (Schemes 1.2 and 1.3). NMR studies of 2, 5, 8, and 11 indicate dearomatization, as the pyridine protons are shifted to lower frequency (olefinic region). Moreover, the structure of complex 2 is unequivocally corroborated by single-crystal X-ray diffraction studies [23]. Importantly, the dearomatized complexes of 2, 5, and 8 activate dihydrogen by cooperation between the rathenium center and the deprotonated phosphine arm, resulting in aromatization to quantitatively yield the ruthenium traws-dihydride complexes of 3, 6, and 9, respectively (Schemes 1.2). The magnetically equivalent... 

Tridentate bis(oxazolinyl)pyridinyl rhodium and ruthenium pincer complexes are useful as catalysts for hydrosilylations and cyclopropanations. These NNN-type inorganic pincer complexes are not as stable, however, as phosphine or salen-type pincer complexes. On the other hand, an organometallic tridentate bis(oxazolinyl) phenyl NCN-type complex is stable. These optically active NCN-type pincer complexes act as efficient catalysts for enantioselective hetero Diels-Alder reactions of Danishefsky s diene with glyoxylates [26]. 

A wide range of ruthenium and osmium complexes incorporating metallated pincer phosphines or pincer amines have been prepared and characterized and used in applications ranging from materials to catalysis. These will not be reviewed in great detail here—for information, readers are referred to the following citations. ... 

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