Complex sentence: He was especially friendly with the painters Monet and Manet, collected Impressionist paintings before Impressionism became fashionable, and a number of such paintings from his personal collection are now housed in some of the world's leading art museums.
Split into simpler sentences: He was especially friendly with the painters Monet and Manet, and collected Impressionist paintings before Impressionism became fashionable. A number of such paintings from his personal collection are now housed in some of the world's leading art museums.