Kinetic studies on the reactions of HCl with trans-[MoLCNPh)(Ph2PCH2CH2PPh2)2] (L=N2, H2, or CO)

The kinetics of the reactions between anhydrous HCl and trans-[MoL(CNPh)(Ph2PCH2CH2PPh2)(2)] (L = CO, N-2 or H-2) have been studied in thf at 25.0 degreesC. When L = CO, the product is [MoH(CO)(CNPh)(Ph2PCH2CH2PPh2)(2)]'. and when L = H-2 or N-2 the product is trans-[MoCl(CNHPh)(Ph2PCH2CH2PPh2)(2)]. Using stopped-flow spectrophotometry reveals that the protonation chemistry of trans-[MoL(CNPh)(Ph2PCH2CH2PPh2)(2)] is complicated. It is proposed that in all cases protonation occurs initially at the nitrogen atom of the isonitrile ligand to form trans-[MoL(CNHPh)(Ph2PCH2CH2PPh2)(2)] Only when L = N-2 is this single protonation sufficient to labilise L to dissociation. and subsequent binding of Cl gives trans-[MoCl(CNHPh)(Ph2PCH2CH2PPh2)(2)]. At high concentrations of HCl a second protonation occurs which inhibits the Substitution. It is proposed that this second proton binds to the dinitrogen ligand. When L = CO or H,, a second protonation is also observed but in these cases the second protonation is proposed to occur at the carbon atom of the aminocarbyne ligand, generating trans[MoL(CHNHPh)(Ph2PCH2CH2PPh2)(2)](2+). Addition of the second proton labilises the trans-H-2 to dissociation, and subsequent rapid binding of Cl and dissociation of a proton yields the product trans-[MoCl(CNHPh)(Ph2PCH2CH2PPh2)(2)]. Dissociation of L = CO does not occur from trans-[Mo(CO)(CHNHPh)(Ph2PCH2CH2PPh2)(2)](2-), but rather migration of the proton from carbon to molybdenum. and dissociation of the other proton produces [MoH(CO)(CNPh)(Ph2PCH2CH2PPh2)(2)]'. (C) 2002 Elsevier Science B.V. All rights reserved.