N,N',N'-[Tris(trimethylsilyl)]hydrazino(dichloro)arsane, (Me3Si)(2)N-N(SiMe3)-AsCl2 (1), has been transformed into the corresponding N-trimethylsi lyl-N',N'-bis-(dimethylchlorosilyl) hydrazi nod i methyl arsane in a two-step synthesis: (i) Addition of GaCl3 to 1 results in the formation of the corresponding hydrazinodimethylarsane GaCl3 adduct (2). (ii) Reaction of 2 with 4-(dimethylamino)pyridine (DMAP) yielded the adduct-free hydrazinoclimethylarsane (3). The intriguing methyl/chlorine exchange with GaCl3 as transfer/exchange reagent represents a new synthetic route to the hitherto unknown N-tri methylsilyl-N',N'-bis-(dimethylchlorosilyl) hyd razi nod i In ethylarsane in contrast to the same reaction of the phosphorus analogue that results in the formation of triazadiphospholes. The new exchange reaction was unambiguously proven by NMR and X-ray studies (1: monoclinic, P2(1)/c, a = 9.5002(19) angstrom, b = 13.840(3) angstrom, c = 17.226(5) angstrom, = 120.12(2)degrees; V 1959.1(8) angstrom(3), Z = 4; 2: orthorhombic, Pbca; a 11.7766(2) A, b = 13.9927(2) angstrom, c 28.3298(4) angstrom; V 4668.37(12) angstrom(3), Z = 4; 3: monoclinic, P2(1)/c, a 12.015(2) A, b = 12.466(3) angstrom, c 13.031(3) angstrom, = 98.20(3)degrees; V = 1931.8(7) angstrom(3), Z = 4). Structural comparisons of the hydrazinoarsanes with their GaCl3 adducts provide interesting similarities and differences. Computations at the B3LYP level reveal that the exchange process is -34 kcal/mol exergonic.