PENTADIENYL METAL PHOSPHINE CHEMISTRY .10. COMPARISON OF THE REACTIONS OF (ETA-5-PENTADIENYL)MN[(ME2PCH2)3CME] AND (ETA-5-2,4-DIMETHYLPENTADIENYL)RE(PME2PH)3 WITH H+ - ISOLATION OF A PROTONATED MANGANESE COMPLEX CONTAINING AN AGOSTIC C-H-M INTERACTION