Insertion Reactions of (PPh<sub>3</sub>)<sub>2</sub>Pt(SR)<sub>2</sub> with CS<sub>2</sub>, where R = H, CMe<sub>3</sub>, CHMe<sub>2</sub>, 4-C<sub>6</sub>H<sub>4</sub>Me; Structure of (PPh<sub>3</sub>)Pt(SC<sub>6</sub>H<sub>4</sub>Me)(S<sub>2</sub>CS-4-C<sub>6</sub>H<sub>4</sub>Me)