The novel phosphido complexes [thf(ArO)3WPM(CO)5] (3 a,b; Ar=2,6-Me2C6H3; M=W, Cr; 3 a is depicted here) can be prepared in high yields by the reaction of [W2(OAr)6] with tBuCP in the presence of [M(CO)5thf]. Initial reactivity studies with [(ArO)4W=O] and [(Ph3P)2Pt(2-C2H4)] resulted in the formation of dinuclear four-membered ring complexes and indicated the high side-on reactivity of these compounds. Theoretical studies of the model complexes [(HO)3WP], [(HO)3WPW(CO)5], and [thf(HO)3WPW(CO)5] give insights into the bonding situation.