Tertiary Phosphine Adducts of Manganese(i1) Dialkyls. Part 2. ' Synthesis, Properties, and Structures of Monomeric Complexes t

Monomeric tetrahedral manganese dialkyl tertiary phosphine complexes of stoicheiometry MnR2 ( PR'3)2 have been identified in solutions by electron spin resonance spectra and the alkyl complex Mn(CH,CMe,Ph), ( PMe3), isolated and structurally characterised by X-ray crystallography. The molecule has a severely distorted tetrahedral geometry with P-Mn-P and C-Mn-C angles of 96.2 and 137.9 ' respectively, which reflect the relative sizes of the two kinds of ligand. The Mn-C and Mn-P distances are 2.1 49(6) and 2.633(4) A respectively. Use of the chelating phosphine, 1,2- bis(dimethy1phosphino)ethane (dmpe), has allowed the isolation of the tetrahedral monomers MnR,(dmpe) (R = CH,SiMe3, CH2CMe3, and CH,Ph). The chelate dialkyl o-xylylene, o-(CH2),C6H4, gives an octahedral complex Mn[o-(CH2),C6H4] (dmpe), whose structure has also been determined by X-ray diffraction. In this molecule, all metal-ligand bond lengths are shorter than the corresponding bonds in Mn(CH2CMe2Ph)2(PMe3)2. This is consistent with a significant reduction in the Mn " radius on adoption of the low-spin state observed. The Mn-C distances are 2.1 1 O(5) and 2.1 04(6) A, while the Mn-P distances of 2.230(3) (trans to P) and 2.298(3) a (trans to C) reflect the different trans-influence abilities of alkyls and phosphines. The X-band e.s.r. spectra of the monomeric complexes have been studied in detail and are discussed in terms of distorted tetrahedral high-spin MnI1 and octahedra