1,3-Diaryltriazenes, ArN:N·NHAr, react with hydrido or low-oxidation state phosphine complexes of the platinum metals to afford products containing monodentate or chelate 1,3-diaryltriazenido (ArNNNAr–) ligands. Highly coloured, air stable, crystalline products synthesised in this manner include 1,3-diaryltriazenido derivatives of ruthenium :Ru(ArNNNAr)2(PPh3)2, RuH(ArNNNAr)(CO)(PPh3)2, RuCl(ArNNNAr)(CO)(PPh3)2; osmium: Os-(ArNNNAr)2(PPh3)2, OsH(ArNNNAr)(CO)(PPh3)2, OsH3(ArNNNAr)(PPh3)2; rhodium: RhH2(ArNNNAr)(PPh3)2, Rh(ArNNNAr)3, RhCl(ArNNNAr)2(PPh3), Rh(NO)(ArNNNAr)2(PPh3), Rh(ArNNNAr)(CO)(PPh3)2[Rh(Ph2PCH2CH2PPh2)2][ArNNNAr]; iridium: IrH2(ArNNNAr)(PPh3)2, IrHCl(ArNNNAr)(PPh3)2; palladium; cis- and trans-Pd(ArNNNAr)2(PPh3)2; and platinum: cis- and trans-Pt(ArNNNAr)2(PPh3)2, Pt(ArNNNAr)2[Ph2P(CH2)nPPh2](n= 2–4), and PtCl(ArNNNAr)(PR3)2(R = Et or Ph). The new complexes are characterised, and their stereochemistry determined, by i.r. and n.m.r. spectroscopy.