(Dimethylarsino)phenylchromium tricarbonyl as a source of (benzyne)chromium tricarbonyl. The novel structures of Ru3(CO)8(.mu.-H){.mu.3-.eta.2-[(.eta.6-C6H4)Cr(CO)3]}(.mu.-AsMe2) and Ru2(CO)6(.mu.-H){.mu.-.eta.2-[(.eta.6-C6H4)Cr(CO)3]}(.mu.-AsMe2)