1,2-Ferrocenediylazaphosphinines: An Unusual Coordination Behavior and Application to Allylic Alkylation
Thanh Thien Co, Seung Whan Paek, Sang Chul Shim, Chan Sik Cho, and Tae-Jeong Kim
Organometallics 2003, 22, 1475 - 1482
Abstract:
The reaction of 1,2-ferrocenediylazaphosphinines (1a, R1 = H; 1b, R1 = Me; 1c, R1 = Ph) with M(CO)6 (M = Mo, W), MX(CO)5 (M = Mn, Re; X = Br, Cl), and [Pd(3-C3H5)Cl]2 shows a strong tendency to adopt an unusual chelating bidentate coordination through nitrogen and the carbonyl oxygen, yielding M(2-N,O)(CO)4 (2, M = Mo; 3, M = W), M(2-N,O)(X)(CO)3 (6, M = Mn, X = Br; 7, M = Re, X = Cl), and [Pd(2-N,O)(3-C3H5)]BF4 (after treatment with AgBF4) (8), respectively. X-ray crystallographic structure determinations of 3a (R1 = H) and 8a (R1 = H) show the formation of a five-membered metallacycle with the distance of the metal-carbonyl oxygen bond being shorter than that of the metal-nitrogen bond in both compounds. The complexes 2 and 3 further undergo oxidative addition with allyl iodide to yield the corresponding M(II) complexes of the type [M(2-N,O)( 3-C3H5)(I)(CO)2] (4, M = Mo; 5, M = W). Complexes 2-5 and 8 were employed as catalysts for nucleophilic allylic substitution of allyl acetates as a probe for both regio- and enantioselectivities of the reaction. All reactions involving unsymmetrical allyl acetates (E)-RCH=CHCH2OAc (R = Pr, Ph) led exclusively to the formation of achiral linear product (E)-RCH=CHCH2Nu regardless of the type of catalysts, the ligand, or the allyl substrate employed. One exception to the above statement is the observation that Mo- and W-based catalysts (2-5) are totally inactive toward the allylic substitution of cinnamyl acetate (R = Ph). Asymmetric allylic alkylation of a symmetrically 1,3-disubstituted substrate, PhCH=CHCH(OAc)Ph, is accomplished only by Pd-catalysts (8) with enantiomeric excesses up to 50% ee.
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