Chemicals that Decrease fertility
Numerous chemicals are linked with decreasing male fertility. 
In fact, studies suggest that unhealthy lifestyles and environmental factors (e.g. plasticisers in the water system) may be causing this decrease in fertility. 
See: http://www.telegraph.co.uk/men/active/mens-health/10695991/Why-are-mens-sperm-rates-falling.html etc
Obviously conclusive studies are limited at this stage. 

But if you want to be more specific, I recall that chloroform is known to cause miscarriages and sterility in mice. Googling that to find a citation led me to this article:
http://www.ncbi.nlm.nih.gov/pubmed/10969727
Which found evidence of an otherwise non-toxic antifertility agent for male rats. 

To be honest, I would be surprised to find studies which have tested a anti-fertility drug on men. Such a thing should not make it past an ethics board (given the ability to prevent impregnation by far less drastic measures, e.g. condoms). 



If however you were talking about the sort of chemical castration they did to someone like Alan Turing, they were not designed to sterilise him (heck, his 'crime' was homosexuality and children were not a likely outcome of that), but to alter his hormones and personality. Anyway, modern drugs might be something like Cyproterone acetate or Depot medroxyprogesterone acetate - though that is also used as a birth control drug for women.