The reaction of the 1,2-dihalodiborane(4) B 2 (NMe 2 ) 2 Cl 2 with the lithium tungsten salts Li[(η 5 -C 5 H 5 )(R 3 P)(OC) 2 W] [R = Me (3a), Ph (3b)] yields via alkali salt elimination the phosphinesubstituted diborane(4)yl tungsten complexes [(η 5 -C 5 H 5 )(R 3 P)(OC) 2 W-{B(NMe 2 )-B(NMe 2 )Cl}] [R = Me (4a), Ph (4b)]. Both compounds have been fully characterized in solution by NMR and IR spectroscopy and 4a additionally by X-ray diffraction analysis.