N,N',N'-[Tris(trimethylsilyl)]hydrazino(dichloro)arsane, (Me3Si)2N-N(SiMe3)-AsCl2 (1), has been transformed into the corresponding N-trimethylsilyl-N',N'-bis-(dimethylchlorosilyl)hydrazinodimethylarsane 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 hydrazinodimethylarsane (3). The intriguing methyl/chlorine exchange with GaCl3 as transfer/exchange reagent represents a new synthetic route to the hitherto unknown N-trimethylsilyl-N',N'-bis-(dimethylchlorosilyl)hydrazinodimethylarsane 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) A, b = 13.840(3) A, c = 17.226(5) A, beta = 120.12(2) degrees ; V = 1959.1(8) A3, Z = 4; 2: orthorhombic, Pbca; a = 11.7766(2) A, b = 13.9927(2) A, c = 28.3298(4) A; V = 4668.37(12) A3, Z = 4; 3: monoclinic, P2(1)/c, a = 12.015(2) A, b = 12.466(3) A, c = 13.031(3) A, beta = 98.20(3) degrees ; V = 1931.8(7) A3, 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.