Mononuclear NHC−Pd−π-Allyl Complexes Containing Weakly Coordinating Ligands

Attempts are described to synthesize ionic 14 e [(π-allyl)Pd(NHC)]Y complexes (NHC = C(N( t Bu)CH) 2, C(N(C 6 H 3 -2,6- i Pr 2 )CH) 2 ). Reaction of {(η 3 -2-RC 3 H 4 )Pd(μ-Cl)} 2 (R = H, Me) with AgOTf yields polymeric, helical {(η 3 -C 3 H 5 )Pd(μ-OTf)} n ( 5a ) and dimeric {(η 3 -2-MeC 3 H 4 )Pd(μ-OTf)} 2 ( 5b ). Treatment of (η 3 -2-RC 3 H 4 )Pd(NHC)Cl (R = H, Me) ( 6a − d ) with LiMe or (tmeda)MgMe 2 affords the Pd−methyl complexes (η 3 -2-RC 3 H 4 )Pd(NHC)CH 3 ( 7a − d ). Adduct formation of 5a, b with NHC, metathesis of 6a − d with AgOTf, and protolysis of 7c, d with HOTf yield the triflate complexes (η 3 -2-RC 3 H 4 )Pd(NHC)(OTf) ( 8a − d ), whereas protolysis of 7a, b with acids (HOTf, HBF 4 ) results in complex degradation. From the reactions of 6a, c with AgBF 4 in THF, and AgPF 6 and AgAlR F 4 (R F = OC(CF 3 ) 3 ) in THF and CH 2 Cl 2, respectively, the ionic THF-solvates [(η 3 -C 3 H 5 )Pd{C(N( t Bu)CH) 2 }(THF)]Y (Y = BF 4, 9a(BF 4 ); PF 6, 9a(PF 6 ); Al{OC(CF 3 ) 3 } 4, 9a(AlR F 4 ) ) and [(η 3 -C 3 H 5 )Pd{C(N(C 6 H 3 -2,6- i Pr 2 )CH) 2 }(THF)]Y (Y = BF 4, 9c(BF 4 ); PF 6, 9c(PF 6 ) ) and the CH 2 Cl 2 -solvates [(η 3 -C 3 H 5 )Pd{C(N( t Bu)CH) 2 }(CH 2 Cl 2 )]AlR F 4 ( 11a(AlR F 4 ) ) and [(η 3 -C 3 H 5 )Pd{C(N(C 6 H 3 -2,6- i Pr 2 )CH) 2 }(CH 2 Cl 2 )]PF 6 ·2CH 2 Cl 2 ( 11c(PF 6 ) ) have been isolated. In contrast, reaction of 6a, c with AgBF 4 in toluene or CH 2 Cl 2 yields the neutral solvent-free BF 4 adducts (η 3 -C 3 H 5 )Pd{C(N( t Bu)CH) 2 }(BF 4 ) ( 12a ) and (η 3 -C 3 H 5 )Pd{C(N(C 6 H 3 -2,6- i Pr 2 )CH) 2 }(BF 4 ) ( 12c ), consistent with the marked nucleophilicity of the BF 4 anion. Drying the CH 2 Cl 2 -solvates 11a, c(Y) (Y = PF 6, AlR F 4 ) at ambient temperature under vacuum affords the PF 6 and AlR F 4 adducts (η 3 -C 3 H 5 )Pd{C(N( t Bu)CH) 2 }(PF 6 ) ( 13a ), (η 3 -C 3 H 5 )Pd{C(N(C 6 H 3 -2,6- i Pr 2 )CH) 2 }(PF 6 ) ( 13c ), (η 3 -C 3 H 5 )Pd{C(N( t Bu)CH) 2 }(AlR F 4 ) ( 14a ), and (η 3 -C 3 H 5 )Pd{C(N(C 6 H 3 -2,6- i Pr 2 )CH) 2 }(AlR F 4 ) ( 14c ). Reaction of 8 − 14 with water produces the (nonisolated) water adducts [(η 3 -C 3 H 5 )Pd(NHC)(H 2 O)]Y ( 10a − d(Y) ). The molecular structures of 5a, 9a(BF 4 ), 11c(PF 6 ), and 12a have been determined. The various anions and solvate ligands are arranged in their order of donor strength/nucleophilicity toward the [(π-allyl)Pd(NHC)] + moiety.