Tetraacetatodirhodium(II) complexes with tris(methoxyphenyl)phosphines, their reactivity, structure, and antitumor activity

Reactions of [Rh-2(mu -OAc)(4)(H2O)(2)] ([1 . (H2O)(2)]) with tris(3-methox yphenyl)phosphine at 1:1 and 1:2 molar ratios yield, first, the appropriate adducts: [1 . (H2O){P(C6H4-3-OMe)(3)}] and [1 . {P(C6H4-3-OMe)(3)}(2)], an d then [Rh-2(mu -OAc)(3){mu-(C6H3-3-OMe)P(C6H4-3-OMe)(2)}(HOAc)(2)] ([2 . ( HOAc)(2)]), and [Rh-2(mu -OAc)(2){mu-(C6H3-3-OMe)P(C6H4-3-OMe)(2)}(2)(HOAc) (2)] ([3 . (HOAc)(2)]) complexes, respectively. They have been characterize d by spectroscopic methods. The molecular structure of [3 . (HOAc)(H2O)] ha s been determined crystallographically. The complexes [3 . (HOAc)(2)], [Rh- 2(mu -OAc)(3){mu-(C6H3-4-OMe)P(C6H4-4-OMe)(2)}(HOAc)(2)] ([4 . (HOAc)(2)]), and [Rh-2(mu -OAc)(2){mu-(C6H3-4-OMe)P(C6H4-4-OMe)(2)}(2)(HOAc)(2)] ([5 . (HOAc)(2)]) reversibly react with CO giving mono- and biadducts. Antitumor activity of binuclear rhodium(II) compounds [3 . (HOAc)(2)], [Rh-2(mu -OAc) (3){mu-(C6H3-2-O)P(C6H3-2-OMe)(2)}(HOAc)] ([6 . (HOAc)]), and [Rh-2(mu -OAc )(3){mu-(C6H3-6-OMe-2-O)P[(C6H3-2,6-(OMe)(2)](2)}(HOAc)] ([7 . (HOAc)]) hav e been investigated in vitro. The most active agent for investigated tumor lines is complex [6 . (HOAc)]. It shows higher activity than cisplatin (cis -[PtCl2(NH3)(2)]). Antitumor activity decreases in the series: [6 . (HOAc)] > [7 . (HOAc)] > [3 . (HOAc)(2)]. Activity of all investigated rhodium(II) complexes is higher than that of [1 . (H2O)(2)].