Complexes trans-[MH(CN)L₂] 1 {L = PPh₂(CH₂)_nPPh₂, n = 1 (dppm), 2 (dppe) or 3 (dppp), and PR₂CH₂CH₂PR₂, R = Et (depe) or para-tolyl (dtpe), M = Fe (for dppe, depe and dtpe only), Ru or Os} were prepared by displacing with cyanide the halide from trans-[MH(X)L₂], X = Br or Cl, or dihydrogen from trans-[Ru(H₂)H(dppe)₂]BPh₄. Systematic trends in the IR and ¹H, ³¹P and ¹³C NMR and electrochemical properties are noted. The addition of one equivalent of HOTf (HO₃SCF₃) or [HPPh₃]OTf to trans-[MH(CN)L₂] 1 with n = 1, 2 or 3 usually produces the hydrogen isocyanide complexes trans-[MH(CNH)L₂]OTf 2. The use of ¹³CN⁻ or C¹⁵N⁻ in compounds 1 provides evidence for the MCNH coordination mode over MNCH. Protonation at the M–H bond to give dihydrogen complexes trans-[M(H₂)(CN)L₂]⁺ occurs to a small degree for M = Ru, n = 1 or 3, in CH₂Cl₂ and completely for M = Os, L = depe. The use of HBF₄· Et₂O results in a variety of products including trans-[MH(CNH)L₂]BF₄2*, trans-[MH(CNBF₃)L₂] and trans-[M(H₂)(CNBF₃)L₂]⁺. The dihydrogen ligand in the last compound with M = Ru, L = dppp, is readily replaced by η¹-BF₄⁻. Structures of the compounds 2 (M = Ru, L = dppe), trans-[RuH(CNBF₃)(dppe)₂] and 2* (M = Os, L = dppe) are reported. The CNH ligand is a good hydrogen-bond donor so that NH⋯O or NH⋯F hydrogen bonds with the counter ion are formed. The reaction of BPh₄⁻ with the CNH ligand of 2 (M = Ru, L = dppe) produces trans-[Ru(H)(CNBPh₃)(dppe)₂], the structure of which is reported. Therefore the CNH ligand reacts readily with BX₄⁻ (X = F or Ph) to produce CNBX₃⁻ ligands and HX.