SYNTHESIS AND CHARACTERIZATION OF ALKYNE COMPLEXES ANALOGOUS TO ZEISESALT - [K(18-CR-6)][PTCL3((PRC)-PR-N-CH)], THE FIRST COMPLEX OF PLATINUM(II) WITH A TERMINAL ALKYNE

The reaction of K-2[PtCl4] with crown ether 18-cr-6 yields in methylen e dichloride [K(18-cr-6)](2)[PtCl4] (2) and in water [K(18-cr-6)](2)[P t2Cl6] (3). 3 reacts with alkynes with internal triple bonds to give a lkyne complexes of Zeise's salt type [K(18-cr-6>][PtCl3][(RC=CR')] [R, R' = Me, Me (4a); Et, Et (4b); Me, Et (4c); Me, Pr-n (4d); Ph, Ph (4e ); C(OH)Me(2), C(OH)Me(2) (4f)]. Complexes 4a-f (T-dec 130-186 degrees C) were characterized by elemental analysis as well as by NMR, IR and Raman spectroscopy. Due to coordination of the alkyne to PtCl3- vibra tion frequencies V(C=C) are lowered to 1937-2059 cm(-1) corresponding to a relative lowering Delta v/v of about 10%. The molecular structure s of 4a (monoclinic, P2(1)/m, a = 8.795(2), b = 11.447(3), c = 12.544( 2) Angstrom, beta = 109.66(2)degrees, Z = 2, R(1) = 0.0292) and 4b (tr iclinic, P $($) over bar$$ 1, a = 9.172(2), b = 10.918(3), c = 14.645( 4) Angstrom, alpha = 98.32(2), beta = 99.43(2), gamma = 112.67(2)degre es, Z = 2, R(1) = 0.0401) were elucidated by X-ray analysis. The angle between the planes PtCl3 and Pt(C=C) in 4a is exactly 90 degrees and in 4b it is 81 degrees. The lengthening of the C=C bond is small in ac cordance with ab initio MO calculations reflecting the dominance of si gma donation over pi back-donation. The K-Cl-trans distance in 4a is v ery short (3.077(4) Angstrom and the angle between the mean plane of t he crown ether and the PtCl3 group is only 20.9 degrees. In 4b there i s a contact of K to Cl-trans (3.126(5) Angstrom) and Cl-tris (3.356(6) Angstrom) whereas the interplanar angle PtCl3/18-cr-6 amounts to 105. 5 degrees. Complexes 4 can be interconverted by ligand substitution re actions and the equilibirium constant for 4a and 4b is K = 3.02. Thus [K(18-cr-6)][PtCl3((PrC)-Pr-n=CH)] (4g) was prepared by treatment of 4 a with 1-pentyne at -20 degrees C. 4g (T-dec 95 degrees C), the first platinum(II) complex containing an alkyne with a terminal triple bond, was characterized by elemental analysis and spectroscopically (V(C=C) 1937 cm(-1), (2)J(Pt,H) 70.6 Hz). Complexes 4 react with ethylene to give [K(18-cr-6)][PtCl3(H2C=CH2)] (5) representing Zeise's salt in whi ch the potassium cation is coordinated by a crown ether.