ATTEMPTED SYNTHESES OF TRANSITION-METAL AND LANTHANIDE (DIALKYLAMINO)SQUARATES - THE HYDROLYSIS PROBLEM

Reaction of 1-amino-2-methoxycyclobutenedione with M(NO3)(2). xH(2)O ( M = Mn, Co, Ni, Cu, Zn) in aqueous solution results in the formation o f the squarates M(C4O4). 4H(2)O and/or M(C4O4). 2H(2)O owing to the hy drolysis of both the methoxy and amino groups on the ligand. Similarly , reaction of this ligand with M(NO3)(3). 6H(2)O (M La, Eu, Gd, Tb) re sults in the formation of the respective lanthanide squarates. Bufferi ng the reactant solutions at different pH's did not change the results and neither did using the alternative solvents methanol, ethanol, pro pan-1-ol, and acetonitrile. In previously reported reactions between 1 -amino-2-methoxycyclobutenedione and 1-(dimethylamino)-2-methoxycyclob utenedione separately with Pb(NO3)(2) under similar reaction condition s, the amino groups remained unhydrolyzed. The substituent amino group s also remain unhydrolyzed when these ligands are left to stand in aqu eous solution in the absence of transition metal ions; only the methox y group is hydrolyzed. 1-(Dimethylamino)-2-hydroxycyclobutenedione (1) , formed from such a hydrolysis of 1-(dimethylamino)-2-methoxycyclobut enedione in aqueous solution, crystallizes in space group P2(1)/c, wit h a = 5.093(1) Angstrom, b = 8.331(1) Angstrom, c = 15.087(3) Angstrom , beta = 95.12(1)degrees, and Z=4. However, attempts at complexation o f the ligand with Mn(II) ions resulted in the formation of a mixture o f the Mn(II) squarate Mn(C4O4). 4H(2)O and the salt [Mn(H2O)(6)][HC4O3 NH2](2). 2H(2)O (2), in which the amino group remains intact. Compound 2 crystallizes in the tetragonal space group P4(2)/m with a = 7.251(3 ) Angstrom, 15.979(8) Angstrom, and Z = 2. If tetraethylammonium amino squarate is used instead of 1-amino-2-methoxycyclobutenedione, both [C o(C4O4)(H2O)(4)] and [CO(C4O4)(H2O)(2)] are formed On reaction with Co (NO3)(2). 6H(2)O. Hydrolysis of the amino group also occurs when the h igher homologue 1-(dimethylamino)-2-methoxycyclobutenedione is reacted with Co(NO3). 6H(2)O, bur only [Co(C4O4)(H2O)(2)] is formed. [Co(C4O4 )(H2O)(2)] crystallizes in the space group Pn (3) over bar n with a = 16.256(1) Angstrom and Z = 24 and is isomorphous with [Co(C4O4)(H2O)(2 )]. 0.33H(2)O, which has been reported previously. Evidence suggests t hat the hydrolysis of the dialkylamino substituents in the 1-(dialkyla mino)-2-methoxycyclobutenediones is apparently mediated by the transit ion and lanthanide metals. The use of the hydrolysis of the amino grou p in 1-dialkylamino derivatives of squaric acid as a convenient synthe tic tool is discussed.