Unexpected selectivity in electrophilic attack on (PNP)RuN

Abstract: Protonation of (PNP)RuN, where PNP is (tBu2PCH2SiMe2)2N, with HCl occurs at the amide nitrogen, with coordination of chloride to RuIV, 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 C2v 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. [Copyright &y& Elsevier]