Kinetische Untersuchungen über Substitutionsreaktionen an Metallkomplexen. 9. Mitteilung [1]. Kinetik und Mechanismus der Reaktion von Hexamethylborazolchrom‐tricarbonyl mit tertiären Phosphinen und Phosphiten [2]

Abstract

Abstract Hexamethylborazolechromium tricarbonyl B 3 N 3 (CH 3 ) 6 Cr(CO) 3 reacts with tertiary phosphines and phosphites under surprisingly mild conditions by cleavage of the ring‐to‐metal bond. For L = trialkylphosphines and trialkyl‐ or triaryl‐phosphites, compounds of the general composition cis ‐Cr(CO) 3 L 3 are formed, whereas for L = triphenyl‐ and tricyclohexyl‐phosphine the complexes trans ‐Cr(CO) 4 L 2 are obtained. The kinetics of the reaction of B 3 N 3 (CH 3 ) 6 Cr(CO) 3 with phosphites P(OR) 3 (R = CH 3 , C 2 H 5 , C 6 H 5 ) have been studied by means of spectrophotometric methods. The second‐order rate law indicates a primary, rate‐determining attack of the phosphite to either the metal atom or the ring ligand of the borazole complex. This attack is favoured by an extremely low activation energy. The mechanism of the substitution process is discussed in detail, and the reactivity of the hexamethylborazole compound is compared with that of other half‐sandwich type complexes.