Three different azaferrocenes (Cp*FePyr) have been prepared which vary in the numberof alpha-methyl substituents on the pyrrolyl ring, and hence the stericenvironment of the Nitrogen-donor:  These azaferrocenes are PMAF (Pyr = pyrrolyl), 6MAF (Pyr = 2-methylpyrrolyl) and HMAF (2,5-dimethylpyrrolyl.  The boraneadducts (BX3; X = H, F, Cl, C6F5 and 9-bora-bicyclo[3.3.1]nonane (9-BBNH)) of these azaferrocenes have been synthesized and characterized by IR and NMR spectroscopy and, in some cases, X-ray crystallography.  In this set, only the HMAF adduct of 9-BBNH has not been isolated, presumably due to steric hinderance of the alpha-methyl groups in HMAF.  However, with the smaller acceptor, BF3, no difference in N-B bond length is found between the X-ray structures of PMAF-BF3 and HMAF-BF3.  The structure of HMAF-B(C6F5)3 was also determined and shows a classical Lewis acid-base adduct albeit with considerable distortion of the azaferrocene moiety.  19F and 1H NMR solution studies show that the azaferrocene-B(C6F5)3 adducts remain intact in solution and display restricted rotation about N-B and/or B-C bonds:  The lack of reactivity of these adducts with H2(g) also supports the conclusion that these are not frustrated Lewis acid/base pairs.  Efforts to further increase the steric bulk of the azaferrocene Lewis base will be outlined as will other reactivity studies of these borane adducts.  Electrochemical characterization of HMAF and 6MAF will also be reported.

Varying the sterics of an azaferrocene Lewis base donor: Synthesis and structures of azaferrocene-boranes

247th National Meeting (2014)

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