No abstract

Square-planar palladium complexes containing tridentate ligands with PXP (X = C, N, O, S, and As) donor sets have been prepared. For [Pd(POP-R)(CH3CN)2l(BF4)2 complexes (where POP-R is bis((diethylphosphino)ethyl) ether, bis((diphenylphosphino)ethyl) ether, or bis((dicyclohexylphosphino)ethyl) ether), the POP-R ligands function as bidentate ligands.

Pd(triphosphine)(CH&N)I(BF4)2 complexes have been prepared with mesityl or trimethoxybenzene substituents on the central phosphorus atom of the triphosphine ligand. An X-ray diffraction study of [Pd(MesetpE)(CH&N)](BF& (where MesetpE is bis((diethy1phosphino)ethyl)mesitylphosphine) has been completed. [Pd(MesetpE)(CH&N)I(BF4)2 crystallizes in the space group Pi with a = 10.370(2) A, b = 11.009(2) A, c = 14.483(2) A, cx = 103.203(13)", p = 92.748(16)", y = 92.556(15)", V = 1605.2(5) Hi3, and 2 = 2. The structure was refined to R = 0.0659 and R, = 0.0771 for 4467 independent reflections with F > 4dF). The cation has a square-planar structure with one methyl group of the central mesityl substituent blocking one potential coordination site. Kinetic studies of this complex in dimethylformamide indicate that the rate-determining step is the reaction of the [Pd-(MesetpE)(DMF)l+ cation with C02. Comparison of the rate constants for this and other mesityl-substituted complexes with those of other [Pd(triphosphine)(CH&N)](BF4)2 complexes suggests that all proceed through a five-coordinate transition state.

The reactions of the water-soluble chelating phosphines 1,2-bis(bis(hydroxyalkyl)phosphino)ethane (alkyl = n-propyl, DHPrPE; n-butyl, DHBuPE; n-pentyl, DHPePE) with FeCl(2).4H(2)O and FeSO(4).7H(2)O were studied as routes to water-soluble complexes that will bind small molecules, dinitrogen in particular. The products that form and their stereochemistry depend on the solvent, the counteranion, and the alkyl chain length on the phosphine. In alcoholic solvents, the reaction of FeCl(2).4H(2)O with 2 equiv of DHBuPE or DHPePE gave trans-Fe(L(2))(2)Cl(2). The analogous reactions in water with DHBuPE and DHPePE gave only cis products, and the reaction of FeSO(4).7H(2)O with any of the phosphines gave only cis-Fe(L(2))(2)SO(4). These results are interpreted as follows. The trans stereochemistry of the products from the reactions of FeCl(2).4H(2)O in alcohols is suggested to be the consequence of the trans geometry of the Fe(H(2)O)(4)Cl(2) complex, i.e., substitution of the water molecules by the phosphines retains the geometry of the starting material. The formation of cis-Fe(DHPrPE)(2)Cl(2) is an exception to this result because the coordination of two -OH groups forms two six-membered rings, as shown in the X-ray structure of the molecule. DHBuPE and DHPePE reacted with FeSO(4).7H(2)O in water to initially yield cis-Fe(P(2))(2)SO(4) compounds, but subsequent substitution reactions occurred over several hours to give sequentially trans-Fe(DHBuPE)(2)(H(2)O)(SO(4)) and then trans-[Fe(DHBuPE)(2)(H(2)O)(2)]SO(4). The rate constants and activation reactions for these aquation reactions were determined and are consistent with dissociatively activated mechanisms. The cis- and trans-Fe(L(2))(2)X (X = (Cl)(2) or SO(4)) complexes react with N(2), CO, and CH(3)CN to yield trans complexes with bound N(2), CO, or CH(3)CN. The crystal structures of the cis-Fe(DHPrPE)(2)SO(4), trans-Fe(DHPrPE)(2)(CO)SO(4), trans-Fe(DHBuPE)(2)Cl(2), trans-[Fe(DHBuPE)(2)(CO)(Cl)][B(C(6)H(5))(4)], trans-Fe(DMeOPrPE)(2)Cl(2), trans-Fe(DMeOPrPE)(2)Br(2), and trans-[Fe(DHBuPE)(2)Cl(2)]Cl complexes are reported. As expected from using water-soluble phosphines, the complexes reported herein are water soluble (generally greater than 0.5 M at 23 degrees C).