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).