The synthesis and characterization of N-heterocyclic carbene (NHC) and cyclic (alkyl)(amino)carbene (cAAC) complexes of molybdenum(IV) and tungsten(IV) chloride is reported. Reaction of two equivalents of the NHCs IMes (1,3-bis(2,4,6-trimethylphenyl)imidazolin-2-ylidene), IDipp (1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene) and IiPr^Me (1,3-diisopropyl-4,5-dimethylimidazolin-2-ylidene) with [MCl₄(SEt)₂] (M = Mo, W) in toluene afforded the bis-NHC complexes [MCl₄(NHC)₂] (M = Mo: NHC = IMes 1, NHC = IMes 2; M = W: NHC = IMes 3, NHC = IDipp 4, NHC = IiPr^Me5). Mono-carbene complexes [MCl₄(NHC)(SEt₂)] 6–9 (M = Mo: NHC = IMes 6, NHC = IMes 7; M = W: NHC = IMes 8, NHC = IDipp 9) are available via ligand dismutation of 1–4 with [MCl₄(SEt)₂]. Complexes 1–9 were characterized by using elemental analysis, IR- and multinuclear NMR spectroscopy and X-ray diffraction for 1–8. The reactivity of the mono-NHC complexes 6–9 towards the cyclic (alkyl)(amino)carbene cAAC^Me as well as the two electron donor ligands trimethylphosphine, triphenylphosphine, pyridine (py) and N,N-dimethylpyridin-4-amine (DMAP) was studied, which led to the synthesis of the mixed substituted complexes [MCl₄(NHC)(cAAC^Me)] (M = Mo: NHC = IMes 10, NHC = IDipp 11; M = W: NHC = IMes 12, NHC = IDipp 13), [MCl₄(NHC)(PR₃)] (M = W: NHC = IMes, R = Me 14, NHC = IMes, R = Ph 15, NHC = IDipp, R = Me 16, NHC = IDipp, R = Ph 17), [MCl₄(NHC)(py)] (M = Mo: NHC = IMes 18, NHC = IDipp 20; M = W: NHC = IMes 22, NHC = IDipp 24) and [MCl₄(NHC)(DMAP)] (M = Mo: NHC = IMes 19, NHC = IDipp 21; M = W: NHC = IMes 23, NHC = IDipp 25).