Crystal structures of o-, m,- and p-nitrophenylferrocenes and their relevance to other sterically crowded phenylferrocenes

Abstract

The crystal structures of the nitrophenylferrocenes [Fe(η-C₅H₅)(η-C₅H₄R)][R =o-(1), m-(2), or p-O₂NC₆H₄(3)] have been determined. All three structures consist of discrete molecules with the iron atom η⁵-bonded to both cyclopentadienyl rings with bond lengths in the range 1.997(9)–2.120(10)Å. The steric constraints of the nitro group lead to different conformations in the three structures. Thus in the ortho structure, the o-nitro group intersects the phenyl ring at angle (Θ′) of 42.3(1)° and the phenyl ring intersects the cyclopentadienyl (cp) ring at an angle (Θ) of 43.6(1)°. Corresponding angles in the less crowded meta and para structures are 10.3(1), 17.4(1)(meta) and 2.9(1), 12.5(1)°(para) respectively. These structures are discussed in conjunction with that of 2,2′,5,5′-tetramethyl-1,1′-bis(2″,4″,6″-trimethylphenyl)ferrocene, (4), and other ortho-substituted phenylferrocenes. Iron-57 Mössbauer and ¹³C n.m.r. data for (4) are presented and discussed. The ¹³C data have been used in an estimation of Θ for a number of ortho-substituted phenylferrocenes. A critical survey of known structures of ferrocene derivatives is also presented.