M onodentate, Semicarbazone, Thiosem icarbazone, But-2-yne, Tungsten(II) Reaction of [W I(C O )(N C M e)(dppm )(772 -M eC2M e)][BF4] {dppm = Ph2 P(C H 2 )PPh2} with an equim olar quantity of L {L = R R 'C N N H C O N H 2 (R = R ' = Me; R = H, R ' = Ph)} or L {L = R R 'C N N H C S N H 2 (R = R ' = Me, Et; R = Me, R ' = E t, Pr", Bu', Ph; R = H, R ' = Ph)} gives the m onodentately coordinated sem icarbazone or thiosem icarbazone products [W I(CO)L(dppm)(?7 2 -M eC2M e)][BF4] (1 -9 ) . 13C N M R spectroscopy suggests that the but-2 -yne ligand is donating four electrons to the tungsten in [W I(CO){H(Ph)CNN H CSN H 2 }(dppm)(?7 2 -M eC2M e)][BF4].