Abstract: A catalyst composition comprising a solution of an organo-metallic complex of platinum or rhodium in a liquid allyl ether which has a b.p. of at least 150.degree. C. at 1 bar and which is free from groups having an adverse effect on the catalytic affect of the complex; polyorganosiloxane coating compositions containing a Si--H polysiloxane and a polysiloxane containing Si--OH, Si-vinyl or Si-allyl groups, an organo-metallic complex of platinum or rhodium and an allyl ether as defined above; and the use of the compositions for preparing release coatings on substrates.In the coating of substrates, especially paper, with release coatings based on heat-curable polysiloxane compositions, organo-metallic complexes of platinum or rhodium can be used as catalysts provided they are dissolved in the composition. The low-boiling solvents hitherto used have disadvantages in causing atmospheric pollution and requiring solvent-recovery plant.