Catalyzes the dehydrogenation of precorrin-2 to form sirohydrochlorin which is used as a precursor in both siroheme biosynthesis and in the anaerobic branch of adenosylcobalamin biosynthesis. It is unable to oxidize precorrin-3. NAD(+) + precorrin-2 = 2 H(+) + NADH + sirohydrochlorin Cofactor biosynthesis; adenosylcobalamin biosynthesis; sirohydrochlorin from precorrin-2: step 1/1. Porphyrin-containing compound metabolism; siroheme biosynthesis; sirohydrochlorin from precorrin-2: step 1/1. Homodimer. Belongs to the precorrin-2 dehydrogenase / sirohydrochlorin ferrochelatase family.