Diethycyanamide complexes [M(N?CNEt 2 )(CO) n L 5 - n ]BPh 4 (1a-5a) [M = Mn, Re; n = 1, 2, 3; L = PPh(OEt) 2 , P(OEt) 3 ] were prepared by allowing hydrides MH(CO) n L 5 - n to react first with triflic acid (HOTf) and then with an excess of diethylcyanamide. The related cyanoguanidine derivatives [M{N?CN(H)C(NH 2 )?NH}(CO) n L 5 - n ]BPh 4 (1b-4b) were prepared by reacting hydrides MH(CO) n L 5 - n first with an equivalent of HOTf and then with an excess of cyanamide N?CNH 2 or, alternatively, with cyanoguanidine. Bis(diethylcyanamide) complexes MBr(N?CNEt 2 ) 2 (CO) 3 (6, 7) were prepared by allowing pentacarbonyl species MBr(CO) 5 to react with an excess of cyanamide N?CNEt 2 . The complexes were characterised by spectroscopy (IR, 1 H, 3 1 P, 1 3 C NMR) and by X-ray crystal structure determination of [Mn(N?CNEt 2 )(CO) 2 {PPh(OEt) 2 } 3 ]BPh 4 (2a) and ReBr(N?CNEt 2 ) 2 (CO) 3 (7a).