Unexpected selectivity in electrophilic attack on (PNP)RuN
摘要:
Protonation of (PNP) RuN, where PNP is ((Bu2PCH2SiMe2)-Bu-t)(2)N, with HCl occurs at the amide nitrogen, with coordination of chloride to Ru-IV, while triflic acid protonates the same nitrogen, but has triflate anion hydrogen-bonded to the proton on the PNP amide nitrogen, not triflate coordinated to the metal. Methyl triflate however alkylates the nitride nitrogen, to give a C-2v symmetric product. DFT calculations show that the thermodyamic preference is for proton on amide nitrogen while alkyl favors nitride alkylation, even without the need for a hydrogen bond to reverse the H vs. alkyl preference. Alkylation at the amide nitrogen leads to nearly complete loss of the PN(R)P Ru/N bond in this unobserved isomer. These preferences among nucleophilic sites on (PNP)RuN are rationalized based on the frontier orbitals of this molecule. (C) 2008 Elsevier B.V. All rights reserved.