The reactions of MoCl₅, 1, with small amounts of a series of carbonyl compounds in a chlorinated solvent were investigated. The chloroiminium salts [ClCHNEt₂][Mo(O)Cl₄{OC(H)NEt₂}], 2a, and [ClCNH(CH₂)₄CH₂][Mo(O)Cl₄{OCNH(CH₂)₄CH₂}], 2b, were obtained by a selective 1:2 molar reaction of 1 with, respectively, N,N-diethylformamide or ε-caprolactam. Otherwise 1 reacted with tetra-N-alkyl ureas in a 1:2 ratio to give the Mo(IV) mononuclear complexes MoCl₄(urea)₂ [urea = (Me₂N)₂CO, 3a; urea = (Et₂N)₂CO, 3b; urea = (EtPhN)₂CO, 3c] in high yields. Addition of 2 equiv. of ketones to 1 resulted in clean formation of equimolar amounts of MoOCl₃(OCR₂) (R = Me, 4a; R = Et, 4b; R = Ph, 4c) and R₂CCl₂. Analogously 1,2-C₆H₄(Me)(CHCl₂) was produced from MoCl₅ and ortho-tolyaldehyde. The reactions of 1 with 1H-indole-2,3-dione (isatin) took place with selective chlorination of the carbonyl function non-adjacent to the nitrogen: the complexes MoOCl₃(3,3-dichloro-2,3-dihydro-1H-indol-2-one)₂, 5a, and MoOCl₃(isatin)(3,3-dichloro-2,3-dihydro-1H-indol-2-one), 5b, were isolated depending on the stoichiometry employed. The X-ray molecular structures of 2b, 3b, 4b, 5a and 5b were ascertained.