Redox transmetallation of Tl(C5H4PPh2) with an excess of Sm in refluxing thf (thf = tetrahydrofuran) or Eu in dme (dme = 1,2-dimethoxyethane) at room temperature gave the lanthanoid(II) compounds [Sm(C5H4PPh2)2] (1) and [Eu(C5H4PPh2)2(dme)] (2). Crystallization of (1) or [Yb(C5H4PPh2)2(dme)] with OPPh3 in dme yielded [Sm(C5H4PPh2)2(OPPh 3)2] (3) and [Yb(C5H4PPh2)2(OPPh 3)2] (4). Room-temperature transmetallation of Tl(C5H4PPh2) with Nd gave the lanthanoid(III) compound (Nd(C5H4PPh2)3(thf)] (5), but analogous reactions with La, Pr, Er, Gd and Y in refluxing thf generally gave intractable oils, although in one instance impure [La(C5H4PPh2)3(thf)].(thf) 0.5, namely (6).(thf)0.5, was isolated. This complex was also obtained at room temperature by using LaI3-activated La metal. Oxidation of (1) with 1 equiv. of Tl(C5H4PPh2) in toluene yielded solvent-free Sm(C5H4PPh2)3 (7). Addition of OPPh3 to these systems allowed the isolation of [Ln(C5H4PPh2)3(OPPh 3)].(thf)x (x = 0-1.5; Ln = La (8), Pr (9), Nd (10), Sm (11), Er (12), Y (13)). Single-crystal X-ray structure determination of (10).(thf)1.5, (11).(thf)1.5 and (12).(thf)1.5 revealed formally 10-coordinate complexes with an O-bonded OPPh3, three η5-C5H4PPh2 ligands and lattice thf. The centroids of the C5 rings and the oxygen atom surround the central metal in a distorted tetrahedral array.