Coordinatively unsaturated diiron complexes: Synthesis and crystal structures of [Fe-2(CO)(4)(mu-H)(mu-(PBu2)-Bu-t)(mu-Ph2PCH2PPh2)] and [Fe-2(CO)(4)(mu-CH2)(mu-H) (mu-(PBu2)-Bu-t)(mu-Ph2PCH2PPh2)]

[Fe-2(mu-CO)(CO)(6)(mu-H)(mu-(PBu2)-Bu-t)] (1) reacts spontaneously with dp pm (dppm = Ph2PCH2PPh2) to give [Fe-2(mu-CO) (CO)(4)(mu-H)(mu-(PBu2)-Bu-t)( mu-dppm)] (2 c). By thermolysis or photolysis, 2 c loses very easily one ca rbonyl ligand and yields the corresponding electronically and coordinativel y unsaturated complex [Fe-2(CO)(4)(mu-H)(mu-(PBu2)-Bu-t)(mu-dppm)] (3). 3 e xhibits a Fe-Fe double bond which could be confirmed by the addition of met hylene to the corresponding di-metallacyclopropane [Fe-2(CO)(4)(mu-CH2)(mu- H)(mu-(PBu2)-Bu-t)(mu-dppm)] (4). The reaction of 1 with dppe (Ph2PC2H4PPh2 ) affords [Fe-2(mu-CO)(CO)(4)(mu-H)(mu-(PBu2)-Bu-t)(mu-dppe)] (5). In contr ast to the thermolysis of 2 c, yielding 3, the heating of 5 in toluene lead s rapidly to complete decomposition. The reaction of 1 with PPh3 yields [Fe -2(CO)(6)(H)(mu-(PBu2)-Bu-t)(PPh3)] (6a), while with (Bu2PH)-Bu-t the compo und [Fe-2(mu-CO)(CO)(5)(mu-H)(mu-(PBu2)-Bu-t)((Bu2PH)-Bu-t)] (6b) is formed . The thermolysis of 6b affords [Fe-2(CO)(5)(mu-(PBu2)-Bu-t)(2)] and the de gradation products [Fe(CO)(3)((Bu2PH)-Bu-t)(2)] and [Fe(CO)(4)((Bu2PH)-Bu-t )]. The molecular structures of 3, 4 and 6b were determined by X-ray crysta l structure analyses.