Kollmar, Herbert Max Planck Institute for Medical Research, Max Planck Society;
http://www.sciencedirect.com/science/article/pii/0040402072881225/pdf?md5=6d1e9ce48a131cf2ec6bdc93e893c301&pid=1-s2.0-0040402072881225-main.pdf (Any fulltext)
https://doi.org/10.1016/0040-4020(72)88122-5 (Any fulltext)
Kollmar, H. (1972). MO calculations on electrophilic reactions—II: The addition of hydrogen to methylene, a carbene insertion Process. Tetrahedron, 27(24), 5893-5901. doi:10.1016/0040-4020(72)88122-5.