Synthesis and molecular structure of the organometallic zwitterion (η5-C5H3MeBCl3)Fe(CO)3:: evidence for alternative sites of nucleophilicity within the [(η5-C5R5)Fe(CO)2]- anion

The organometallic zwitterion (eta(5)-C5H3MeBCl3)Fe(CO)(3) (2) is isolated as a minor product from the reaction between the sodium salt of the anion [(eta(5)-C5H4Me)Fe(CO)(2)](-) and boron trichloride. The crystal structure of 2 [P2(1)/n, a = 7.3927(5) Angstrom, b = 13.8027(9) Angstrom, c = 12.2759(9) Angstrom, alpha = gamma = 90degrees, beta = 92.517(3)degrees] features discrete molecules in which the coordination sphere of the iron center comprises three carbonyls and a novel (eta(5)-C5H3MeBCl3) ligand, derived from attack of BCl3 on the (eta(5)-C5H4Me) moiety of the parent compound. The isolation of 2 confirms that the nucleophilic properties of organometallic anions of the type [(eta(5)-C5R5)M(CO)(n)](-) (M = Fe, Ru, n = 2; M = Mo, W, n = 3) are not confined to the metal center, or to the carbonyl oxygens (examples of which have previously been reported) but also encompass the cyclopentadienyl ligand.