The stable primary phosphine complexes trans-M(PH(2)Mes*)(2)Cl-2 (1, M = Pd; 2, M = Pt; Mes* = 2,4,5-(tBU)(3)C6H2) were prepared from Pd(PhCN)(2)Cl-2 and K2PtCl4, respectively. Reaction of Pt(COD)Cl-2 (COD = 1,5-cyclooctadiene) with less bulky arylphosphines gives the unstable cis-Pt(PH2Ar)(2)Cl-2 (3, Ar = Is = 2,4,6-(iPr)(3)C6H2; 4, Ar = Mes 2,4,5-Me(3)C(6)H(2)). Spontaneous dehydrochlorination of 4 or direct reaction of K2PtCl4 with 2 equiv of PH(2)Mes gives the insoluble primary phosphido-bridged dimer [Pt(PH(2)Mes)(mu-PHMes)Cl](2) (5), which was characterized spectroscopically, including solid-state P-31 NMR studies. The reversible reaction of 5 with PH(2)Mes gives Pt(PH(2)Mes)(2)(mu-PHMes)](2)[Cl](2) (6) while PEt(3) yields [Pt(PEt(3))(2)(mu-PHMes)](2)[Cl](2) (7), which on recrystallization forms [Pt(PEt(3))(mu-PHMes)Cl](2) (8). Complex 5 and PPh(3) afford [Pt(PPh(3))(mu-PHMes)Cl](2) (9). Addition of 1,2-bis(diphenylphosphino)ethane (dppe) to 5 gives the dicationic [Pt(dppe)(mu-PHMes)](2)[Cl](2) (10-Cl), which was also obtained as the tetrafluoroborate salt 10-BF4 by deprotonation of [Pt(dppe)(PH(2)Mes)Cl[BF4] (11) with Et(3)N or by reaction of [Pt(dppe)(mu-OH)](2)[BF4](2) with 2 equiv of PH(2)Mes. Complexes 8, 9, and 10-Cl . 2CH(2)Cl(2) . 2H(2)O were characterized crystallographically.