Reactivity of mixed cyclometalated palladium compounds containing the [2-Me2NC6H4C(H)SiMe3] monoanion. Part 2. Transmetalation reaction and formation of a novel .mu.-alkylidene compound (x-ray) bis(.mu.-chloro)bis{.mu.-C,.sigma.-N-[2-(dimethylamino)benzylidene](.mu.-chloro)(diethyl sulfide)dipalladium(II)}