A method comprising: (i) admixing allyl alcohol with CO and H 2 to form a starting material mixture; and (ii) reacting the starting material mixture in the presence of a catalyst under conditions capable of forming a product mixture comprising 4-hydroxybutanal and 2-methyl-3-hydroxypropanal; wherein the catalyst is a transition metal complex comprising a transition metal ion and a diphosphine ligand and wherein the ratio of 4-hydroxybutanal to 2-methyl-3-hydroxypropanal in the product mixture is less than 1.5:1, and the starting material mixture optionally comprises a phosphine(C 3-30 ) or a substituted phosphine (C3-30) ; and wherein the diphosphine ligand has a bite angle from - 85° to - 95° and the diphosphine ligand has the formula: wherein: R 1 , R 2 , R 1 ', and R 2 ' are each independently selected from aryl (C6-12) or substituted aryl (C6-12) ; R 3 , R 4 , R 3 ', and R 4 ' are each independently selected from hydrogen, alkyl (C1-12) , substituted alkyl (C1-12) , aryl (C6-12) , or substituted aryl (C6-12) ; R 5 is alkyl (C1-12) , substituted alkyl (C1-12) , aryl (C6-12) , or substituted aryl (C6-12) ; or is taken together with R 6 and is alkanediyl (C1-6) or substituted alkanediyl (C1-6) ; R 5 ' is alkyl (C1-12) , substituted alkyl (C1-12) , aryl (C6-12) , or substituted aryl (C6-12) ; or is taken together with R 6 ' and is alkanediyl (C1-6) or substituted alkanediyl (C1-6) ; R 6 is alkyl (C1-12) , substituted alkyl (C1-12) , aryl (C6-12) , or substituted aryl (C6-12) ; is taken together with R 5 and is alkanediyl (C1-6) or substituted alkanediyl (C1-6) ; or is taken together with R 6 ' and is alkanediyl (C1-6) or substituted alkanediyl (C1-6) ; and R 6 ' is alkyl (C1-12) , substituted alkyl (C1-12) , aryl (C6-12) , or substituted aryl (C6-12) ; is taken together with R 5 ' and is alkanediyl (C1-6) or substituted alkanediyl (C1-6) ; or is taken together with R 6 and is alkanediyl (C1-6) or substituted alkanediyl (C1-6) . (i) admixing allyl alcohol with CO and H 2 to form a starting material mixture; and (ii) reacting the starting material mixture in the presence of a catalyst under conditions capable of forming a product mixture comprising 4-hydroxybutanal and 2-methyl-3-hydroxypropanal; R 1 , R 2 , R 1 ', and R 2 ' are each independently selected from aryl (C6-12) or substituted aryl (C6-12) ; R 3 , R 4 , R 3 ', and R 4 ' are each independently selected from hydrogen, alkyl (C1-12) , substituted alkyl (C1-12) , aryl (C6-12) , or substituted aryl (C6-12) ; R 5 is alkyl (C1-12) , substituted alkyl (C1-12) , aryl (C6-12) , or substituted aryl (C6-12) ; or is taken together with R 6 and is alkanediyl (C1-6) or substituted alkanediyl (C1-6) ; R 5 ' is alkyl (C1-12) , substituted alkyl (C1-12) , aryl (C6-12) , or substituted aryl (C6-12) ; or is taken together with R 6 ' and is alkanediyl (C1-6) or substituted alkanediyl (C1-6) ; R 6 is alkyl (C1-12) , substituted alkyl (C1-12) , aryl (C6-12) , or substituted aryl (C6-12) ; is taken together with R 5 and is alkanediyl (C1-6) or substituted alkanediyl (C1-6) ; or is taken together with R 6 ' and is alkanediyl (C1-6) or substituted alkanediyl (C1-6) ; and R 6 ' is alkyl (C1-12) , substituted alkyl (C1-12) , aryl (C6-12) , or substituted aryl (C6-12) ; is taken together with R 5 ' and is alkanediyl (C1-6) or substituted alkanediyl (C1-6) ; or is taken together with R 6 and is alkanediyl (C1-6) or substituted alkanediyl (C1-6) . <EOS>