Interaction of allylic alcohols with halogeno-bridged platinum(II) complexes [Pt2X4(PR3)2](X = Cl or Br) and [NBun4]2[Pt2Cl6] : crystal structure of [PtCl2(PMe2Ph)(CH2CHCH2OH)]

Abstract

A series of complexes of type cis-[PtCl₂(PR₃)Q](PR₃= PMe₃, PEt₃, PPrⁿ₃, or PMe₂Ph; Q = prop-2-en-1-ol, but-1-en-3-ol, or 3-methylbut-1-en-3-ol) have been prepared. The crystal structure of cis-[PtCl₂(PMe₂Ph)-(CH₂CHCH₂OH)] is described : no intramolecular hydrogen bond is present. Crystal data : space group P2₁/n, a= 12.540(3), b= 10.668(7), c= 10.929(2)Å, β= 97.02(2)°, and Z= 4. The complexes cis-[PtCl₂(PR₃)Q] have been studied by variable-temperature ¹H and ³¹P n.m.r. spectroscopy. There is no evidence for rotamers, as found with other olefin complexes. At room temperature slow dissociation to give the bridged complex [Pt₂Cl₄-(PR₃)₂] and the free allyl alcohol occurs. The complex cis-[PtCl₂(PMe₂Ph)(CH₂CHCH₂OH)] does not exchange rapidly with free allyl alcohol and separate resonances due to free and complexed allyl alcohol could be observed : in contrast [NBuⁿ₄][PtCl₃(CH₂CHCH₂OH)] exchanges rapidly with free allyl alcohol on the n.m.r. time scale. N.m.r. studies of the interaction between chloro-bridged complexes of the type [Pt₂Cl₄(PR₃)₂]{and also [Pt₂Br₄(PMe₂Ph)₂]} and allylic alcohols show that at low temperatures the bridged species is rapidly and reversibly converted into trans-[PtCl₂(PR₃)(CH₂CHCR¹R²OH)] together with some of the O-bonded species, trans[[graphic omitted]H)]. Above ca. 260 K the resonances start to broaden due to exchange with the bridged complex and have also become much less intense due to reversion back to the bridged complex: cis-[PtCl₂(PR₃)(CH₂CHCR¹R²OH)] is also gradually formed above ca. 260 K. A [Pt₂Br₄(PMe₂Ph)₂]–CH₂CHCH₂OH system also shows the presence of trans-[PtBr₂(PMe₂Ph)(CH₂CHCH₂OH)] and in this case the cis isomer forms to a detectable extent even at 213 K. The bridged complex [Pt₂Cl₄(PPrⁿBu^t₂)₂] containing the bulky phosphine shows the presence of rotamers at 243 K and with allyl alcohol two rotamers trans-[PtCl₂(PPrⁿBu^t₂)(CH₂CHCH₂OH)] form at 213 K. The ¹H and ³¹P n.m.r. and i.r. data are given and discussed.