novel trivalent organophosphonite ligands having the structure of general formula : wherein r is an alkyl or aryl group containing 1 to 30 carbon atoms ; ar 1 and ar 2 are aryl groups containing 4 to 30 carbon atoms ; r1 to r6 are h or alkyl or aryl hydrocarbon radicals containing 1 to 40 carbon atoms ; and x is a connecting group or a simple chemical bond , were developed and found to be very active for hydroformylation processes for ethylenically unsaturated substrates . catalyst solutions prepared from these ligands with a rh metal show an unusual “ ligand acceleration effect ” for simple alkenes , i . e ., the hydroformylation activity increases as the concentration of ligand increases , and are capable of producing linear or branched aldehydes under typical hydroformylation conditions .